Tick - One of those annoying little machines that jump on you and deal damage.
Seeker - Deals no damage, however alerts other machines to where you are.
Lynx - Smaller robot that moves via a rolling ball. Very annoying.
Runner - Four legged, and small. You'll see these a lot even in the South. Easy to kill, annoying in large combat scenarios.
Hunter - Looks similar to a tank having two legs. However it is noticeably smaller and faster. A few will usually accompany larger machines.
Harvester - Large machine with four legs.
Tank - As previously stated, has two legs. However, it is very large and slow.
Wolf - Large machine rolling on back treads. Mainly fires missiles from its rear compartment.
Firebird - Has 4 large arms extending from a ball. Hovers higher up in the sky.
Reaper - How do I put this... An overpowered tank that loves chaos. Only has a chance of spawning in a region if you have reached threat level 21+ (Will spawn in place of a rival. More on them later.)

Machine Classes:
Apocalypse - Fires bullets that damage the player in other ways. Example: Fire, Radiation, ETC.
FNIX - Noticeable by its red and grey paint job. Killing these will get you closer to different FNIX cosmetic challenges.
Military - Will be camouflage or olive green.
Prototype - Mainly found in the South, just a simple faded orange color.
(If you see any machines fighting, that means one is FNIX/Military and one is Soviet Union. Soviet Union machines will be olive green with a red star somewhere on their body.)

Rivals:
Rivals spawn in an area where you have a higher threat level (every so often) and are pretty good for farming ammo, XP, and that sort of stuff. They travel in hordes of large machines with one more powerful one (you can find the powerful one easily due to its nametag when you hover over it) and also have a few hunters, runners, ETC. with them most of the time. They become stronger and gain more machines every time they level up, which happens gradually with machine-killing activity in the region. However, if you want a Reaper to spawn, (must be at least Threat level 21 in the region,) you must keep that threat level. Every time you kill a rival, your threat level goes down.

Alright, that's it for this guide! Thanks for reading, I hope this helped at least some.