Mentor of the Meek; Entreat the Angels

[MementoMori]

Let's say that at the end of my opponent's turn, I've drawn no cards. I {Cloudshift} a {Captain of the Watch} with a {Mentor of the Meek} in play. I know I might draw {Entreat the Angels}, so I want to keep as much mana open for that as possible - but I also want to draw three cards if I can.

How exactly does Mentor's ability work? Do I have to pay {1} to get his ability to draw a card on the stack at all? Or does it go on the stack regardless, and I choose to pay {1} as it resolves? If it's the latter, then I can miracle Entreat on the first draw and get two more angels out of it, letting the other two triggers go unpaid, than I would if I had to pay for all 3 triggers immediately.

To further complicate it, let's say {Cathars' Crusade} is in play. I can order my triggers such that I draw and cast Entreat before the first Crusade triggers resolve, giving my angels an extra 4 counters, right?

[Keyeto]

The mentor's ability triggers when an appropriate creature enters the battlefield. You choose to pay {1} when the ability resolves. And yes, ordering your triggers correctly would allow you to pump up your angels. The crusade's ability gives the counters when it's trigger resolves.

RESOLVED

[MementoMori]

Glad my instincts were right. I have a pretty good understanding of triggered abilities now, I think. Thanks.

[Keyeto]

Glad to help! Just keep in mind that triggers check the game state for conditions relevant to their effect (in the case if the crusade, a creature etb and then how many creatures you control) twice: Once when placed in the stack, and once upon resolution. If you can remember that, you can use the stack to your advantage like a pro.