Rooftop storm is likely one of those cards wed ask people to cut in upgraded precons, as people optimise the manabase, ramp, zombies, payoffs, draw and interaction, a card enabling you to do a bunch of things for free on top of that is likely not healthy to keep for BC once a deck is upgraded
Don't expect any more bans or unbans for Commander this year
The first thing to consider is the way you want to build a deck
If all of the damage is prevented, the effect of The Rollercrusher Ride's first ability no longer applies
In other words, Elvish Mystic cannot generate more than one mana a turn unless some other card causes it to untap
In this case, the free spell lets you (or another player) create a copy of one of your creatures