There are a few really cool looking Samus' on TurboSquid, however the lowest poly count I could find on any of them is around 17K polies - much too high for a game environment. Realistically, you should be around 2500 polies or so for characters for most games. Some will argue for more than that, but 17,000 is way too many.
In order to use it in a game, you would have to rig it (I believe CharacterFX is now free - you can search for it on these forums) and then animate the joints that you have made/assigned.
Quote: "Also, is there a way to make it shoot out of its cannon arm?"
Sure, this could easily be done. You would simply assign some of the vertices of the cannon to a joint there and use that to obtain the limb angle and location for placement of a projectile. You could assign another joint to the tip of the cannon to place the flash.
Hope this helps.
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