OK, OK, I'll join with an itty-bitty supergenius warrior. Five arms should be plenty, maybe a leg for the heck of it... shoulding go beyond one sword, but... make that three arms, they might get in the way. And the leg should be a water pumb, he needs to be able to move. Much smaller than an amoeba, of course. I'll have to think about what his brain is made out of and where he came from, but he can eat... I have it, he sucks the protoplasm out of amoebas to survive. He doesn't need much, so the amoebas hire him pretty often, and he makes a living.
Name: Apendotripodaquarn (eee for short)
Height: 10 mkm
Limbs: 3 humanoid arms, 1 cyclic pump that makes up half his mass
Weapons: A small graphite blade, 6 mkm in length with a curved, serrated edge
He's not all that smart for a human, but he is smarter than any amoeba.