The spell does need to be cast from your hand, if it gets cast from anywhere else (like with Cascade, for example), Rebound wont trigger, and so to the graveyard with the spell
While lifelink helps soften the blow, that life loss adds up quickly in longer games, especially when facing aggressive pods
To see the full decklist, check out the Fallout Commander deck Mutant Menace here
Sounds simple, but it's actually very, very good
Players of Group Hug decks would answer that question with a few of their own: why are you already thinking of them as your opponents, and is beating all of them actually necessary
It was so far over the line that it got emergency-banned in Standard and is banned in a bunch of formats because it basically warps games around itself