In the Sega classic, The Ooze, there are two endings, a good and a bad ending, which are decided by whether you successfully collected all 50 DNA helixes containing Dr. Cain's DNA. This is a guide to help you find them. Sorry for not including screenshots, I might rectify that in the future.

Except it is, though not part of the original line up. It's a mod you can get via the Steam Workshop, like other Sega classics also not included in this collection, like Chakan: the Forever Man.
This is where you can find the mod by Air Chomp to play this game, it goes over Comix Zone.
https://steamproxy.net/sharedfiles/filedetails/?id=1240606548

This guide was somewhat helpful in getting me started, so I'll give some credit to it. The original information that I copy-pasted I've edited some to be a bit more clear.
https://gamefaqs.gamespot.com/genesis/586357-the-ooze/faqs/42929

Also this portugese youtube channel (I assume portugese because Google translate said so), Azure Galaxy, who posted an Ooze 100% walkthrough that I found incredibly helpful in locating the DNAs. They didn't show every single DNA Helix, just every single one on the path they chose, so I filled in the gaps where necessary.
https://www.youtube.com/c/AzureGalaxyStudios

PART 1
1. On the right side of the first set of fire breathing holes.

2. Shortly after getting the first waypoint, in the lower area, to the right of the Fire-Spitting Machine.

3. After teleporting through that "L" shaped briar patch next to the fire spout, the access point in the angle, you will appear right next to it.

4. Under the extra life surrounded by toxic slag.

5. Under the "L" briar patch mentioned in #3 is another briar patch with a little angle in it just under the "L" patch's angle, which will take you to the first bunny-killing minigame.

PART 2
6. At the very beginning of the stage, to the left by some barrels.

7. After the first fork you can take, there is another fork that goes up or down. Head down, go to the dead end with a frog-slug, and head into one of the divets, the one closest to the "entrance" on the bottom. You will be taken to the bunny killing mini game.

8. Shortly after hitting the switch above the bunny mini game, head to the second fork, take the path that leads left which should also be where a path branches down. There should be a fire breathing hole in the middle of both paths. The helix is there with a slug.

9. Right when you get second waypoint, it should be all the way to the left.

10. At the very end of the level, all the way to the left.

PART 1
Left Entrance
11. In the first room, under the path of the left tractor.

12. In the same room as #11, on the upper left hand corner. Use your punch to get it.

13. In the bunny mini game under a vent under a big obvious grate, shortly after #s 11 and 12.

14. At the 4 way intersection, after the bunny mini game, take the right path and go down through a vent, also under a grate. It should be on the left.

15. In a room with 4 torches and 5 drains. It is hidden between 3 walls.

Middle Entrance
11. Under the path where the first tractor was.

12. Right after #11, all the way to the right should be a pipe that takes you to the bunny mini game.

13. In a small room guarded by an acid nozzle.

14. Shortly after #13, under the path of a moving tractor.

15. Hidden behind a wall with its path blocked by a tractor. The tractor is moving under a vent.


Right Entrance
11. In the corner of a large room. It's guarded by 3 gas nozzles.

12. In a room with a pyro thug, gas trap and 2 torches.

13. From #12, all the way to the left on a slope that falls to some toxic
waste.

14. In the large room covered up by vents, the bunny mini game is accessed by hugging the right wall of a small room located on the upper left corner.

15. After you get out of the large room covered up by vents, there should be a smaller room below it, and a torch below that small room. You can see the DNA Helix covered by the lower wall.

PART 2
Left Path
16. On the left path, along the track above the acid with bomb floaters in the acid and skates on the track, in the upper left area with two trap hatches.

17, 18. In the center-left area, there are two on a platform with acid-thugs and ALOT of trap hatches.

19. At the very end, right next to the exit and amoeba.

20. DO NOT EXIT THE LEVEL! The pipe JUST LEFT of the exit leads to the bunny-killing minigame.

Middle Path
16. Go down the left path (it will look like you can't, the big grey wall is window dressing), and keep going right, not down. In the very tiny and straight alcove is the entrance to the bunny killing minigame.

17. Just below #16, near some bomb floaters, the switch, and some health. Very obvious.

18. On the right path (this wall is also windowdressing), go through the grab-pole maze. It's at the end next to the switch.

19. After hitting both switches and disabling the acid-sprayers, go down and traverse the maze. On the left side, underneath the switch, is the DNA.

20. After hitting the switch in the maze of #19, go all the way right to the grab-pole room. Look in the top-right, by a fire spout.

Right Path
16. On the top most path from the entrance, all the way to the right, in a room with a switch and amoeba.

17. After the switch room from #16, it's in the downward fork with a vacuum, all the way to the left.

18. On the opposite end of the same tube as #17, there is an entrance to a bunny killing minigame.

19. Below where the main path reconnects under the area with #17, in an almost identical manner, but with ameobas.

20. Right under #18, just like it, with a vacuum.

PART 1
21. After a while of playing through the main path, you will find some steam-spitting valves. Between them is your prize.

22. Eventually you will come across the area directly under the area from #21. On the left side, there is a panel that is slightly see through with a violet light. This is the entrance to the bunny-killing minigame.

23. After exiting the area with the minigame, you will see a small passage above you, leading to DNA. DO NOT GRAB IT JUST YET. This room is a trap, with a parasite hidden right beside the passage behind the wall. Get just a tip in and out fast, so that when the parasite launches out of its eggsac it will hit the wall and die instantly. Or, if you have enough mass, instead use a punch to grab it from outside safely.

24. In this area, outside of the passage leading to #23 is an exit to a short maze that leads to a death powerup and an extra life, with parasites between you and it. Along this short maze is DNA.

25. In a room with three steam valves shooting downward, the DNA is right next to them.

PART 2
26. You will come across a pair of doors with corresponding switches guarded by sentry guns. Go through the left door first and progress through it until you flip a switch to open the door to the parasite room, which has the DNA within.

27. When you reach an area filled with filing cabinets and a health pickup, the entrance to the bunny-killing minigame will be one the bottom-left corner, hidden by the wall.

28. In the bottom-left corner of the whole map, guarded by steam valves.

29. In the bottom-center room of the map, with a tiny passage as the entrance and with three spider-bots crawling around.

30. Near the end, there will be a maze of death holes. Carefully go through this, and go past the swirl-maze; this is the exit. Make it past some guardbots and find a corner with some health and a DNA helix right next to it.

PART 1
Top Entrance (left toilet from Level 3 Boss)
31. After progressing normally for a while, you will come across a ramp leading under a grate. Watch out for skitterbots, and the DNA is underneath and obvious.

32. After passing a room with a switch guarded by a fireball launcher, you will find a ramp that connects the entrance to the unified rest of the level. On the right of the passage before this ramp is a piece of wall you can go under. There is a hidden guardbot under it, so kill it first, and then claim your spoil of an equally hidden DNA.

33. Just by the exit, above it, is a coolant pool with a crack in the side. Inside the pool is a DNA.

34. Just by the exit, below it, is a hidden path that leads into a coolant pool. Enter it and keep going downwards. Here is FINALLY that one DNA from the beginning that teased you.

35. JUST ABOVE #24, under the wall that hides the path to it, go right. You will be transported to the bunny killing minigame.

Bottom Entrance (right toilet from Level 3 Boss)
31. In the first room, go upward at the four-way intersection (watch out for enemies) and take the passage to the right. You will come across a wall - it's window dressing, you can pass through it. You're first DNA you can get will be there, above the first one you see and are teased by.

32. Continue left at the four-way intersection and go directly downward. This small dead end has an obvious DNA helix.

33. Just by the exit, above it, is a coolant pool with a crack in the side. Inside the pool is a DNA.

34. Just by the exit, below it, is a hidden path that leads into a coolant pool. Enter it and keep going downwards. Here is FINALLY that one DNA from the beginning that teased you.

35. JUST ABOVE #24, under the wall that hides the path to it, go right. You will be transported to the bunny killing minigame.

PART 2
There is an important task you must do along the way, noted in between with *.

36. After the first ramp downward at the end of the railroad you are on, hit the switch right under and go through the now down energy barrier. Go into the passage just before the second barrier and go past the switch. Go right into the far corner of this alcove for a bunny-killing minigame.

*after hitting the switch at the first four-way intersection with pyro-thugs, backtrack to the extra life you saw before. Hit the switch there and backtrack further to the bottom of the map. You can now go left into a hidden passage and hit a previously inaccessible switch. This will be important later. Proceed normally for now.

37. After a while of regular play, you will go down a ramp onto some green flooring and a pair of guardbots. After killing them both, you will have a choice of up or down. Go to the end of the up path for a DNA.

38, 39. After a second puzzle where you must activate three switches, this time simultaneously activating traps, the DNA will behind the energy barrier to the left they open up. Thanks to you hitting those switches earlier*, the energy barrier right next to it is also down, granting you access to a room with two health pickups and another DNA.

40. At the top-right corner of the map, along the catwalk, you will find a switch next on the right of a four-way intersection. Hit it and go upward. You have now entered the pool below you. For now you can only go left, so go so all the way until you go through the crack to exit it. You will hear a noise like you hit a switch. When you hear that, go all the way right, under the entrance you used to get under the pool to begin with, and through a crack in the pool for the DNA in the very top-right corner of the map.

BE WARNED! This level is confusing because it features transitions from Part 1, to 2, and back to 1 again. These transitions will need to have been made to get all of the DNA, just as a final kick in the balls from a game that's already hard enough. Astute observers will note that Part 2 is actually just all of the elevated parts of Part 1 you could not reach before. Also the exit drain to Part 1 after returning leads directly to Part 3, just for your information, not part 2 again.

PART 1
41. Just right of a blocked off checkpoint near the bottom-center of the map, there is a passage to a switch the opens the way to it. Go to the switch, there will be a DNA next to it.

42. In the top-right corner of the room with the checkpoint mentioned in #41 is a passage to a blocked off maze covered by a grate. Go through it, the DNA is in the middle of it.

*TRANSITION TO PART 2 FROM THE DRAIN IN THE CHECKPOINT AREA MENTIONED ABOVE*

PART 2
43. You will spawn on top of an elevated grate. Go upward to a little outcropping to enter the bunny-killing minigame (which is technically the bunny-killing minigame for part 2, but you will encounter first with this route). There will be FAKE exits all around this minigame, the one you want is in the top-right corner, next to one that is completely blocked off.

*The following is written down along the route I took, but in reality these can be reached in any order, depending on the path the players take.

44. Follow the elevated route you are on, using the teleporters to get around as you go. I took the far-right teleporter. On this path, proceed until you get to a fork, one path going down, another going to an elevated grate that ALSO has a small fork. The upward path of the elevated grate leads to a loop with the DNA at the top, the bottom leads to another teleporter - AVOID THIS TELEPORTER, IT IS THE LEVEL EXIT. backtrack to the previous fork and go down the path you have not yet.

45. Along the downward fork you were instructed to take in #44, is another teleporter. Follow this path and you will immediately find the DNA sitting next to a Super Vacuum.

46. At the end of the path detailed in #45 is another teleporter. You will be teleported to another elevated grate with the DNA obvious, guarded by a Fireball-Thug and a super amoeba.

47. Follow the path as normal, going forward through another teleporter at the end of the section detailed in #46. You will eventually come to a fork going upward and left or right, depending on which side you approach it from, on your path. Go up to find another loop with another DNA, guarded by a fireball-thug, spheroids, and a super amoeba.

*YOU WILL COME TO A CROSS-SHAPED INTERSECTION, THE SAME ONE YOU FIRST TELEPORT TOO WITH THE FIRST TELEPORTATION OF THIS LEVEL. GO ALL THE WAY RIGHT AND FOLLOW A SERIES OF TELEPORTERS THAT WILL TAKE YOU BACK TO THE SPOT WHERE YOU HAVE ACCESS TO THE LEVEL EXIT TELEPORTER YOU WERE INSTRUCTED TO IGNORE IS. TAKE IT AND ENTER THE DOME-TOPPED CONSTRUCT TO TRANSITION BACK TO PART 1.*

PART 1, Second Visit
48. After returning and spawning next to another dome-topped construct, go upward and be careful around the mines to activate a switch. This will open the door to a blocked off section someways directly down from the dome-top. The entrance you are looking for is next to two switches right next to each other and guarded by a super vacuum. Upon entering and going down, there will be a little alcove right when the path turns left to another switch. In the alcove, hidden, is the DNA.

49. Just to the right of the blocked off area mentioned in #48 is an extra life surrounded by holes that will kill you, and just to the right of that, connected by a smaller room, is a path that opens up from a switch found just upward of the extra life. Follow this path until it opens up to a room with super amoebas and two paths upward, one on the left and one on the right, separated by a room with a big drain visible. Go up the one on the left all the way and in the bottom-left corner of the dead-end it opens up to is the entrance to the bunny-killing minigame. This time they try to trip you up by putting in NO obstacles and NO exits - no VISIBLE exits. The exit is actually hidden behind the timer.

50. Proceed to the drain you saw earlier, BUT DO NOT GO THROUGH IT YET. In the bottom-left corner of the room it is in, which is right next to it, is the final DNA.

You got all 50 DNA helixes! Now just kill the directorate, the swine that did this to you to begin with, get your revenge, and claim your reward of the good ending!

The only actualy cheat for this game I could find that didn't involve a Game Genie. Also I have not verified it, but other sources parrot the information. Copy-Pasted from here:
https://gamefaqs.gamespot.com/genesis/586357-the-ooze/cheats

In the options screen, move towards the sound test area (and be careful not to change the default controller scheme). Enter the following list of numbers, and press the C button after setting each one: 009, 019, 010, 024, 011, 013, 006, 027, 006, 088, 003, 030. If done correctly, a sound effect says "Yes!" During gameplay (or in the options menu), hold the A button and then press Start to open the stage select menu.