Once you announce that you're casting a spell, players can't attempt to remove Shimmer Myr from the battlefield to make that casting illegal. Removing Shimmer My after you've cast a spell won't affect that spell.
2020-11-10
Shimmer Myr has no effect on artifact lands because they aren't cast as spells.
Lovlighet:
Standard: Ikke lovlig
Pioneer: Ikke lovlig
Modern: Lovlig
Legacy: Lovlig
Vintage: Lovlig
EDH / Commander: Lovlig
Pauper: Ikke lovlig
Explorer: Ikke lovlig
Historic: Ikke lovlig
Brawl: Ikke lovlig
Premodern: Ikke lovlig
93/94: Ikke lovlig
Shimmer Myr er Lovlig i disse blockene: Scars of Mirrodin