Deathshade Wurm

Burrow {b}
Immunity {g}{g}({g}{g}: Remove a -1/-1 counter from this creature.
Whenever this creature deals combat damage to a player, put X -1/-1 counters on it where X is its toughness minus 1.
Whenever you remove a -1/-1 counter from this creature, put a -1/-1 counter on target creature.