Nanurluk, the Hibernator

Shroud, indestructible
Nanurluk, the Hibernator can't attack or block unless it has five or more +1/+1 counters on it.
Whenever a player casts a spell, put a +1/+1 counter on Nanurluk.
The local tribes learned long ago to step softly and speak in a whisper when in his territory. No invaders have survived to learn that lesson.