Welcome ! I hope this guide will help you get all the achievements in the game!
What makes me fit enough to teach you guys how to get those achievements ? Well, I have all of them and they aren't that hard to get as long as you follow this guide!

Execute a Team Attack.
This one is pretty straight forward. just press E once prompted to near an enemy and you will get it right away, this achievement can be obtained with the achievement "Sister Synergy" if you are playing as Ruby or Yang and do a team attack with them.
At least 2 players are needed for this achievement

Do a Team Attack with Ruby and Yang.
Do a team attack as Ruby assisted by Yang, or the other way around.
This achievement requires at least 2 players.

Play in an online match with all four team RWBY members present.
This achievement requires 4 players, and it's pretty straight forward, everyone just pick one character and start the chapter and it will unlock.

Play in an online match with Jaune, Nora, Pyrrha, and Ren.
Same as above.
This achievement requires the JNPR DLC.

Complete any level without taking damage.
The easiest way to do this is by playing with 3 other friends and let them fight while you stay away from the combat zone. I suggest doing it in a combo with "It's also a gun" since you don't want to get hit, and play on Normal difficulty if you want to do it solo.


The image above is supposed to show you how to do it, just don't jump down when it comes to combat areas, that's it.

Refund all of your Ability Points.
Once you finish your first chapter in the game, press the "refund skill points" button, and this achievement will unlock.

Get an assist on a Mutant Beowolf.
In order to get this achievement you need to give a mutant Beowolf (the green big one) more damage than anyone else, and let a teammate finish him, Basically just give him over 60% damage or more and then let someone kill him for you.
At least 2 players are needed for this achievement.

Collect 10 artifacts during a single play session.
This achievement is player based, YOU yourself need to get 10 artifacts in one single playthrough, if you already know where the artifacts locations are, you can ask your friends to leave them to you, or you can go solo and get 10 of them and this will unlock. There is a guide showing the artifacts locations here: http://steamproxy.net/sharedfiles/filedetails/?id=569745171&tscn=1467923251

Revive a teammate after purchasing Quick Revive.
Revive 5 teammates in order to buy the Quick Revive upgrade, and then use it.
At least 2 players are needed for this achievement.

Get the highest score in a four player online match on a single level.
Show your friends who's boss and top score, you can do this by doing team attacks, kills, revives, turret kills and not dying. Git gud to keep it short. You will need a full lobby.

Reach 100 hits on the combo counter.
This achievement can be done with Yang or Blake since their combos take a while and they are easy to do, I suggest getting Blake and the stun shot skill from the ranged weapon, you can attack them close range and then run away so you won't get hit, and then shoot them from a distance, you need to learn how to counter attack (by pressing F) at the right time, once they are stunned (after the ranged attacks) you can go for hits, to make it even easier for you, Blake has a perk that extends the time before the combo counter resets, this perk is unlocked at level 10. This achievement can be unlocked on singleplayer and it isn't that hard at all especially if you play on higher difficulties, just hit 100 on the combo hit meter, it can be done on any level, I did it on Chapter 7 at the first grimm area. But since the release of Horde Mode that might be your best and easiest option to do it.

Complete Chapter 4 with 3:00 minutes or more left on the clock.
This achievement is fairly easy, all you need to do is stay near the Dust mines and get the dust as fast as possible and run to the bomb and fill it with dust, I suggest using Ruby for this achievement since she is the fastest of the RWBY team.

In a four player online game, each player deposits at least one dust crystal.
It's pretty easy to be fair, just make sure you are in a 4 people lobby and ask them to put the dust in one by one. It can be done at the same time with the "Ticking Time Bomb" achievement but it needs some team communication.

Kill a Mutant Beowolf while your Aura is depleted.
This one is pretty tricky, you DON'T want to have fast aura regen and you definitely want to get the Survivor perk, get the mutant beowulf to low health (like, 3 lines MAX, even lower if possible) let him hit you and once your screen turns red, use your ultimate or just do a combo really fast and this will unlock, it can be done easier with friends if you ask them not to hit him and revive you once you go down.

Complete the campaign in single player.
I used Yang for this one, the ultimate does a lot of damage to the boss, but pretty much every other character can do it. Be careful at his 1 hit kill arrow shots, those can be avoided by dashing to the left or right of him, or by staying at a distance.
If you have already completed the campaign in COOP and haven't gone hunter rank yet, you can skip to last level (Chapter 10) and this achievement will unlock after you defeat the boss since only the last level needs to be finished in order to get the character achievements.
Also, play on Normal if you wanna do it fast.

Complete any level by only using ranged attacks.
It can be done as Blake on the first level of the game. it will be even easier if you are level 10 already and you have the ranged attack perks. This achievement can be unlocked at the same time as "Unscathed" since you won't really want to stay near the grimm when using ranged attacks, duh. Note: Don't even think of slashing even if you didn't attack a monster, you need to ONLY use your ranged attacks.
Note 2: Play on Normal

Get Wave MVP five times in a waved encounter.
This can be achieved on Chapter 5, that's where you will have a 5 waved encounter and you can ask your friends to not attack the mobs as you kill them, simple as that, or again, rock on and show them who's the real MVP.
At least 2 players are needed for this achievement.

Kill 10 enemies with a single Ultimate attack.
This can be done as Yang once you upgrade her "Quake" move to the max, just gather as many grimm as you can and do the "Quake" move in the middle of them, preferably do it on singleplayer on the Eclipse difficulty since you are alone and loads of grimm spawn or just use any high damaging ultimate in Horde Mode.

Get four flawless waves in a waved encounter.
This achievement is best done solo, why ? because you won't have any desync and the grimm will concentrate on you, it can be done with Blake or Ruby in the first chapter or with Blake in the second chapter because grimm only spawn on one side if you go into a far corner, make sure you shoot them and stun them with Blake's skill so they don't go near the Control Centre, if they hit it, then die, you should respawn with a checkpoint, you will know if they hit it or not because a red text will appear saying "The Control Centre is under attack".

I did this twice as Ruby and Blake in Chapter 1, Yang isn't really an option since her attacks aren't ranged so they might go for the Control Centre and Weiss is really slow in comparison.
Consider playing on Normal if you don't want trouble.

Reach Hunter Rank 10.
Well, you have to do the challenges the game gives you and reset your stats 10 times in order to get this achievement ! It hurts, I know.

Here are the challenges I needed to do in order to get Hunter Rank 10. Also be sure to get all the character achievements BEFORE going hunter rank, as this will reset your levels as well and you will need to finish the whole campaign with the rest of the characters, unless a friend hosts the last chapter, in which you will get it after you defeat the boss.

Beat any Horde map solo.
This isn't a hard achievement, just make sure you don't die and let the turrets do the job for you, you can use Blake's stun ranged attack to draw them away from the nodes and stun them. Also, consider playing on Emerald Forest

Collect a total of 20,000 Lien during any Horde match.
You will probably unlock this achievement as you play Horde Mode, you need 20000 Lien in total not 20000 unspent, so spend your Lien and you will get it.

Beat any horde map without building a turret.
Playing on Emerald Forest in 2 PLAYERS is the best bet for this, that is how I got it. You can both play with 2 Blakes or just any character that has the range to draw the enemies away, and then finally DO NOT BUILD ANY TURRETS, also if any of you die near a turret, once you get revived the turret will be built, so watch out for that and also make sure you prioritize on the white robots because they tend to shoot the station even when not aiming at you.

Win any Horde map with all security nodes at 85% health.
I find this achievement easier to get than "The Old Fashioned Way" because you have turrets to back you up, here is how to get it easily, you go into Emerald Forest, (2 players recommended, if both of you are using Blake it will make it easier) you do not buy any turrets until Station 2 and 3, and at Station 2 and 3 just buy 1 shotgun turret for each station, then you and your friend defend the stations and draw the enemies away with ranged attacks, after the 6th wave is done, you will get Station 4 and 5, here you buy all the turrets you can, Station 5 full of shotgun turrets will kill everything mostly. And Station 4 with 2 shotgun turrets near it, 1 grenade launcher turret far away and the rest machine gun turrets will also kill almost everything in sight.
It's that easy, this is literally easier than doing it with no turrets and surviving.

Kill 35 enemies with turrets during a single horde match.
Once you get at least 3500 Lien, build a turret and let it do the work for you, or build even more turrets and let THEM do the work for you!

Have 10 active turrets at once during a horde match.
Get in a lobby of 4 and tell everyone not to spend their Lien until all of you can afford at least 3 turrets, once all of you have enough just build them while a wave is finished or in the middle of it, the turrets will survive long enough in order for you to get 10 of them.

Complete the campaign with each character from TEAM RWBY.
And the 4 TEAM RWBY Characters achievements can be done easily by just getting a character, killing the boss, going back to menu, choose another character, choose last level, beat the boss, and you will gain the Characters achievements, you do not need to go through all the levels again with each character to get the achievements, only the last level needs to be finished with them.

Complete the campaign with each character from TEAM JNPR.
Pretty self explanatory from the achievement above, all goes the same.
Those achievements require the JNPR DLC.

Now... for the real deal... I'm pretty sure most of you are here for the 3 hidden achievements, well, those achievements are REALLY EASY, and here is how to get them.

Cleverly Disguised Jumping Puzzle.
Collect the artifact at the end of the jumping puzzle in Forever Fall.
In Chapter 5, use the key on the door on the right, kill the grimm in the first area and find the jumping puzzle, complete the puzzle and this achievement should unlock.

This achievement is player based as well, YOU need to do it, not your friends to do it for you, if they already have it tell them to leave it to you or just select Chapter 5 from the menu and do it Solo.

Butter and Butter.
Do Blake's taunt right after killing the Mutant Deathstalker.
Taunt as Blake after you kill the boss, simple as that, just press "1" after you kill the Mutant Deathstalker and this achievement will unlock.

Spoiler Alert
Go Team RNJR! Play in an online match with Ruby, Nora, Jaune, and Ren.
This is the same as Go Team RWBY! or Go Team JNPR! only with Team RNJR.
It's probably hidden for obvious reasons, This achievement requires the JNPR DLC.

Thanks everyone for taking a look at this guide and I hope I helped you all achievement hunters out there ! Have I missed anything ? Be sure to let me know in the comments !
Be sure to rate this guide up so others will be able to see it and easily do the achievements !
I will update this guide as soon as possible if new achievements appear in the game or if I have any mistakes still left in everything that's above.