other then that, make upped +2/+2 make it stronger faster
I hope you were kidding there, Disc. I really hope you were.
+2/+2 per other unit is going to be very,
very OP without a powerful curb if you factor in that you can basically use one of this for Aflatoxin bait and another one or two for the killing blow, as Chapuz has mentioned.
BTW, I'm pondering of modifying Disc's idea; basically, it'll become ceil(sqrt(y))/ceil(sqrt(y)) (un)upped, where y is a function linear against the number of other creatures.
FYI, if y = 2x, my scheme makes it still UP (it becomes 7/7, tops).
Also, I'm pondering one thing: if an unupped Bird of Life and an upped Bird of Life are the sole creature on your side of the field, what will happen? Will both die off or stays alive at 1/1?