Delney, Streetwise Lookout - 2W
Legendary Creature - Human Scout (Mythic)
Creatures you control with power 2 or less can't be blocked by creatures with power 3 or greater.
If an ability of a creature you control with power 2 or less triggers, that ability triggers an additional time.
"It's not a matter of what I know. It's a matter of making it worth my while to tell you."
2/2
Yes. Delney will double Mentor's trigger as long as the Mentor's power doesn't get above 2 (the fact that the other creatures entering also have to have power <= 2 matters to Mentor but doesn't directly matter to Delney).
When each trigger resolves, you will separately decide whether to pay 1 to draw a card. The upshot is that you can pay 0 to draw 0, pay 1 to draw 1, or pay 2 to draw 2.