The Dark Tower

The Dark Tower enters tapped unless you control a legendary creature.

When it enters the battlefield, place 6 beam counters on it. Anytime a beam counter is spent, you lose 3 life.

{t}: Gain {c}. Alternatively; You may expend a beam counter as an instant to nullify a spell from an opponent. This can't be countered.

Anytime an effect would destroy it or exile it, you lose a beam counter. Once it is at zero beam counters, you lose.