At the beginning of your upkeep, put a plague counter on Plague Boiler.
: Put a plague counter on Plague Boiler or remove a plague counter from it.
When Plague Boiler has three or more plague counters on it, sacrifice it. If you do, destroy all nonland permanents.
10/1/2005 You choose whether to add or remove a counter when the second ability resolves. You can’t choose to remove a counter if there isn’t one there.
10/1/2005 If the third ability triggers, removing a counter in response won’t stop the effect. However, somehow removing Plague Boiler from the battlefield in response would stop the effect because then you wouldn’t be able to sacrifice Plague Boiler.
10/1/2005 The sacrifice is done on resolution of the triggered ability.