Dies to Removal

The original wording of monstrosity in design was 'once per game', the +1/+1 counters were added to help with the memory issues, but theoretically are not required for a monsterosity ability. By adding +1/+1 counters to it solved both the memory issue and allowed for simpler common monsters that would not be red flagged by NWO.

So technically they could have done
Steve (r)
Creature - weasel
(1)(r)Monstrosity 0.
When steve becomes monstrous it deals 2 damage to target creature or player.
1/1