Tyranid Prime by paying ({1} magic symbol) ({G} magic symbol) ({U} magic symbol) .
When it enters,
Watchful Radstag's evolve ability triggers, putting a +1/+1 counter on it. Its second ability triggers, creating a token copy of it that enters with a number of +1/+1 counters equal to
Master Biomancer's power.
When the token enters, each creature you control's evolve ability will trigger if the token has lesser toughness or power.
Resolve all evolve triggers except those from
Watchful Radstags, putting a +1/+1 counter on each of them.
Resolve a
Watchful Radstag trigger, putting a +1/+1 counter on it. Its second ability triggers, creating a token copy of it that enters with a number of +1/+1 counters equal to
Master Biomancer's power.
Repeat from step 3.
Results
Infinite ETB.
Infinite +1/+1 counters.
Infinite +1/+1 counters on an infinite number of creature tokens.