Standard:
-It should be able to survive in space. Preferably be able to survive any abuse a MKI can.
-It should be able to run fast.
-It shouldn't have too much armor, since that would make it too heavy to be of any use, but it should be able to regenerate from most hits fairly quickly provided it has food, with organic parts to replace any destroyed cybernetics.
-It should be able to obey simple commands, like a well trained attack dog (come here, jump, kill them, stop, go left, stay, be cute, don't eat your teammates, etc.). An implant will allow it to receive commands by radio.
Extras:
-The ability to track people and things through smell and taste.
-Eyes that can see into infrared. Cat-like night vision. Cyberyes with light amps. Cameyes. Something like that.
-It should be able to understand more complex commands.
-It should have implants that allow for a direct video feed of everything it sees.
-It should be able to carry a battlesuit or at least an exoskeleton. Add cybermuscles to handle the weight if necessary.
-It should preferably look lizard-like. Like a big Piecewise or like a big Komodo dragon, but with legs designed to be able to run and jump high.
-It should have some sort of fleshy wings that allow it to glide small distances, something like this:
Common Gliding Lizard-Some redundant systems to increase survivability like partition membranes, secondary heart and brain, etc would be nice.
-It should be able to jump high and climb walls (either with some sort of adhesive or by digging with its claws). Add some sort of spring-like energy accumulation muscles if necessary.
-It should be armored with some kind of lightweight material that will allow it to move fast AND survive light weapons fire like Gauss rifles and laser rifles.
-It should have heavy weapon mounts, for things like gimbal mounted Cutting Lasers, Gauss Cannons or Repeating/Gatling Gauss Rifles. Bonus points if it can use those weapons independently.
-It should have big sharp scary teeth and claws and a scary roar. Bonus points if those can tear light armor apart. Bonus points if it can digest metal and other stuff(within reason) and use them for armor repairs or weapon ammo.
-Bonus points if it can also be used to aid teammates (e.g. carry toolboxes or dispense medical stuff from its teeth-saliva-other organ). It should probably be able to carry artillery and aid in construction in its spare (read: not with a rider) time.
-Extra bonus points if it can breath fire(there are some bacteria that can create a gas that ignites the moment it comes in contact with oxygen but I can't find the article I read it in right now). Super extra bonus points if it can breath namite or white phosphorus or similar. ultra super extra bonus if it can breathe some sort of super oxidizer like chlorine trifluoride. Mega ultra super extra bonus if it can shoot a super heavy laser or high energy projectors from its mouth..