I have quite a few suggestions here, so read on if you have the time!
(Warning: Some of these I have taken from other people's ideas, and added my own twist to them)
DarkBot / InvisiBot: Robot that spawns with a random weapon. Is completely black except for pure white eyes. When you get a certain distance from it, your field of vision is shortened to only a few paces in front of you. The rest is pure black. The only thing visible through the dark fog is DarkBot's White eyes, light swords, arrows and fire weapons.
StatueBot / JetpackBot Mark 3: Looks like an all dark grey version of a mark3 SwordBot. Holds two swords at a time. Each sword can move interdependently to the other. Does not move when it is visible to the player's vision. When it is not visible on screen, it has a Jetpack and can boost at 50% faster than default Jetpack. Has unique sword motion, only available for this robot: a stabbing motion. Jetpacks behind you and will stab you through the chest or decapitate you without you knowing. Spawns in a random position. Freezes in whatever position it is in when player's robot sees it. Does not have a jetpack cool down.
LionBot: Robot shaped as a lion. Jumps twice as high as player. Uses front legs to claw at player and can bite at player. Can jump on player and knock them off Balance. Has teeth and claws made of light sword material. Can be a fire version as well.
HydraBot: A snake-like robot that when sliced in half, creates a clone of itself, unless the head is destroyed. Has Flame Breath. Has little flame spikes on it's back.
SpiderTron7000: Has 6 legs. Has 3, smaller eyes. Two grenade towers. Shoots 8 bombs at a time. Four from each tower, six normal bombs, two shrapnel bombs (explained below) fires bombs sets twice as fast as Spidertron6000. Can walk around. If any robot is stepped on by one of the legs, has the same effect as a light sword. Cannot jump. AI tells it not to walk on jump pad, spikes, saw blade, lava etc, etc.
SpiderTron7500 / Fire SpiderTron: Is the same as SpiderTron7000, except that it launches Fire Bombs (explained Below) at the same rate.
SpiderTron8000: Has 8 legs and 4, even smaller eyes which are half the size of SpiderTron6000. Three grenade towers. Two facing forward, under the main body, one facing upwards. Shoots 12 bombs at a time. Four from each tower, 6 normal bombs, 4 shrapnel bombs (explained below) 2 fire bombs (explained below). Launches bomb sets twice as fast as SpiderTron6000. Can walk around. If any robot is stepped on by one of the legs, has the same effect as a light sword, except for the front two, which have the fire sword effect. Cannot jump. AI tells it not to walk on jump pad, spikes, saw blade, lava etc, etc.
Mark 2 Raptors: More fire from their mouth and a more powerful tail swipe. Maybe they could have some of the flame sword voxels instead of the normal ones for their Teeth, Spikes and Claws? These flame Voxels would act as a sword, too. (say if you swung at it with a sword, and you hit the flame spikes, say, your sword would clash off it like it were another sword) if you walked on top of these flame voxels, your feet would catch on fire.
Baby Raptors: Normal Raptors, except that they are 1/4 the size of normal Raptors. They are faster than the adult Raptors, but have a much smaller flame breath range. Their tail swipe should only be able to knock you down for a second, but due to their size, it could be the last mistake you do with that drone.
Brute Bot: A Robot which carries a level one Hammer (colour: Black) and a Large sword (look below). Each weapon can move independently. Shoots out a random Bomb (Normal, Shrapnel, Fire) every now and then. I think that this model here, done by Skylure, works with it nicely. (She has it labeled as Heavy Drone / Cannon Drone) Otherwise serves as JacobMikeR's Version
TurretBot: An immovable robot, with a thick base. Has a rotating head at the top, which blasts a constant stream of Shrapnel (like the ones from the current SpiderTron Bomb) at the player. It's weak point is it's shooting head, which will explode (like SpiderTron or a Raptor) when hit.
Heal: Upgrade branch from Clone. When dealt a killing blow, your body pixel will fall apart and then rejoin back together, making you the same as you were before you were hit. You will be unable to be damaged for 1 second after. Any enemy robot(s) near you will be disabled for half a second. Can only be used once per level. Can only be used 5 times. Only works when level is active.
Possess: Upgrade branch from Heal. When you die and have no clones, allows you to take over the enemy robot closest to you. You cannot do this again if you die in the taken body. Once you get another clone, and die in the taken body, you may use this ability again. Can only be used 3 times per Human.
Mind Control: Upgrade branch from Possess. When R is pressed the closest enemy robot will turn teams and kill all other robots that are not itself and the player. The mind controlled robot will explode as soon as all other robots are dead (if it didn't already die). Can only be used once per level.
PetBot: Branch upgrade from Mind Control. Allows you to get a small robot dog that follows the player around and attacks the closest enemy. Takes off max of 5 pixels. Can jump the same height as the player. Robots target Petbot only if it attacks them. Every clone after the this upgrade is selected has one PetBot. Cannot have more than one Petbot at the same time, unless you died but your Petbot did not.
Baby Raptors: Can be gotten as a companion. Is a branch off of PetBot.
Raptor Mount: Upgrade Branch from Baby Raptors, and costs two Upgrade Points. Controls as normal. WASD to move, left to use weapon. F to use flame breath, and right click for tail swipe. If you are somehow dis-mounted from your Raptor, you could use something like middle-mouse click button to hop back on, if it is still alive. The Raptor would also have a fully maxed energy bar, which is separate from yours.
Grenade Launcher: Is a gun, shaped like the Spidertron's grenade tower. Rests over the robot's dominant shoulder. Level 1 throws normal bombs, level 2 launches shrapnel bombs (which insta-kill you if caught in blast radius) and level 3 throws Fire Bombs (when the fire bomb explodes, a smaller version of the Spidertron explosion animation will show, and will set any robot caught in the blast on fire). To active the Grenade Launcher by pressing 4. Z and X keys to swap through bomb types. only have a limited amount of Bombs, and more can be gotten from UpgradeBot in exchange for an Upgrade Point.
Larger Sword: an Upgrade for a lager sword. I love the model by Skylure, on this page here (First sword when scrolling down) this sword would be slower than the normal one.
Ground Pound: A Hammer Upgrade. When the hammer hits the ground (or another surface) an array of semi-transparent yellow voxels (like the armour plates) will force themselves up in a temporary wall, which repels all robots, arrows, bombs, fire, etc, etc. in the direction the player is facing. These voxels fly upwards, spinning, and will fall back down vanishing as they hit the ground. The Voxels only exist for about 1.5 seconds.
Duck: Press Q to duck. When using WASD and Q will do a shoulder roll in that direction. SPACE and Q makes the player do a flip in mid air. WASD+SPACE and Q makes player do a leaping dive in the WASD direction, and roll upon landing.
Molten Metal: Like lava. Robots can walk through it, but at half the normal pace. Adds random pixels onto the robot, majorly reducing sensitivity. If in metal for too long the robot will no longer be able to move. Has a dark red or grey colour. The Molten Metal voxels added to the robots will slowly rust off. The voxels would be effected by gravity, and fall to the round and make a pile of random voxels
Molten Metal Thrower: Like the Fire trap, but it throws molten metal. Cannot face upwards. Adds random pixels onto the robot, majorly reducing sensitivity. If in metal for too long the robot will no longer be able to move. The Molten Metal voxels added to the robots will slowly rust off. The voxels would be effected by gravity, and fall to the round and make a pile of random voxels.
More details for humans are shown on the board. Like their gender, Left/Right Handed, where they lived. (left handedness is a 5% chance)
Humans have a 5% chance of their Robot being left handed. (in direct correlation to their info board stats)
SpiderTron4000 models in garbage storage.
Explosions have a small (10%) chance of setting the player on fire if caught in the blast and, will knock over any bots within the blast radius
If a Bot walks into the trail of flame from a jetpack boot, there should be a chance of the bot catching on fire.
If two Hammers collide mid-swing, then some of the normal voxels with be broken off of each Hammer.