Angel, like all bunnies, is as evil as he is cute. When the dastardly plot of the largest bunny organization in the region threatens Fluttershy, he's the best-qualified critter to take them down.
Twilight didn't have to continue "Twilight Time" after the recent fiasco, but she did. The Cutie Mark Crusaders wish to express their thanks by using skills she hasn't taught them to produce a gift for her.