Doorkeeper Thrull

Replacement effects, such as a permanent entering the battlefield tapped or with counters on it, are unaffected. Abilities that apply "as [this permanent] enters the battlefield" are replacement effects.

Look at the permanent as it exists on the battlefield, taking into account continuous effects, to determine whether any triggered abilities will trigger. For example, if you control Opalescence, which says, in part, "Each other non-Aura enchantment is a creature," each enchantment will be a creature at the time it enters the battlefield and will not cause triggered abilities to 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.