By default, there is no limit on how many times per turn a triggered ability can take effect it happens as often as the trigger condition is met
This basically amounts to a damage-free Char if they don't have a way to block or remove it
Theres no Wasteland for the creature decks to combat Grove of the Burnwillows, and the other half of the format just doesnt care at all
When you do cast a spell with convoke, you get to scry two, picking whatever card you want the most to leave on top or even tuck both of them to the bottom of your deck if you don't like either of them
Exiling the creature card with scavenge is part of the cost of activating the scavenge ability
Monica Rambeau / Photon, Living Light Flying and prowess are already potent and it is nice to have the flexibility to play Photon, Living Light right away so we get hexproof