See title, for example [[Generous Patron]]. It’s a long running question I had with a friend, and we kind of came to the conclusion that the answer is no because the creature doesn’t yet exist when the ETB resolves.
But I gave it some thought again because it feels so weird that so many cards have this kind of effect and supposedly it doesn’t get triggered. Does anyone have a definitive answer to this? Would be great if you can refer to the official rulings.
Creatures do count as existing when their ETBs resolve. Generous Patron and similar triggers do count themselves. They count as having entered even before the ETB goes on the stack - see [[Aether Adept]]'s ruling - it can target itself, and targets for abilities are chosen before an ability is put on the stack.
Triggered abilities always go on the stack anyway - even if Generous Patron didn’t count as existing when the ability was triggered (which it does), resolving the next action on the stack requires the current stack action to finish resolving, so it would have to be fully on the battlefield for any abilities triggered by it to be processed.
[[card name]] to call