@luminapinaMage slayer/ready action hits while casting a spell. Should there be a concentration check for all spells, excl. maybe cantrips? readied action takes place after trigger, so first spell then attack. No check needed.
— Mike Mearls (@mikemearls) October 8, 2014
@luminapinaOkay, thank you. So Counterspell is the only way to interrupt the casting of spells with one action or shorter casting times? Correct, at least with what's available in the PHB.
— Mike Mearls (@mikemearls) October 8, 2014
Mage Slayer can attack a caster as a reaction, not a readied action, so wouldn’t this interrupt the caster?
Honorable highband,
Correct, reaction interrupt caster that need a concentration check to finish casting (but not with disadvantage, that is just only concentrating casters)