Sorry to keep flooding with new posts lol. But this just happened to me on cockatrice. Played {sliver legion} then my opponent responds with {orim's chant} and says the legion goes back to my hand. Is that legal? I was like well umm. . . The spell is already cast. But I wasn't sure so I let it go. There's no way this is legal right?
You are right, you already cast the spell.
Once the chant resolves you will not be able to cast spells, this doesn't keep spells that you already cast from resolving.
RESOLVED
Yea that's what I thought. Man some people. . . The other day a guy tried to use a PW ability at instant speed. Couldn't believe it.
The big issue is people don't understand the implications of what they are trying to do. Once they understand just how much their attempted play would destroy the game, then they tend to start learning the rules.
In this case I would respond by telling them: "if that worked I would build a turbo fog deck with that spell and {silence} and I wouldn't just {fog} your attacks, i'd fog your ability to cast spells and stall/ reshuffle till you run out of a library."