Melma Primordiale

This creature attacks each combat if able. At the beginning of your upkeep, put a +1/+1 counter on this creature. Then you may pay {X}, where X is the number of +1/+1 counters on it. If you don't, tap this creature and it deals X damage to you.

The thick, moving mass from the beginning of evolution swallows and digests the animate and inanimate as it unthinkingly strives to continue its existence.