Doorkeeper Thrull

If Doorkeeper Thrull and another creature or an artifact enter the battlefield at the same time, neither one will cause triggered abilities to trigger when they enter the battlefield.

The trigger event doesn't have to specify artifacts or creatures entering the battlefield. For example, Tireless Tracker has an ability that says "Whenever a land enters the battlefield under your control, investigate." If an artifact land or creature land enters the battlefield under your control, that ability won't trigger. If a nonartifact, noncreature land enters the battlefield under your control, the ability will trigger.

Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]." Some keyword abilities are triggered abilities and will have "when," "whenever," or "at the beginning of" in their reminder text.