Clockwork Time Bomb

Infiltrate (This artifact enters the battlefield
under target opponent's control)
Clockwork Time Bomb enters the battlefield
with 5 time counters.
At the beginning of your end step, remove a time counter from Clockwork Time Bomb, then, if it
has no time counters, sacrifice it and lose 12 life.
{4}: Add a time counter to Clockwork Time Bomb.