A caster struck by every projectile from a level 1 magic missile would have to make 3 consecutive DC10 concentration checks. Even assuming they have a +2 Constitution modifier, that has a 72% chance of breaking their concentration. An upcast magic missile could easily shred through legendary resistances.
Does stun break concentration?
Edit- other conditions such as paralyzed, petrified, stunned, and unconscious also include incapacitated in their effects, so they would also break concentration.
Does Magic missile require concentration?
Magic Missile only requires one concentration check, because the spell is a single source of damage. The fact that the darts “strike simultaneously” reinforces this narrative.
When is a concentration check required to cast a spell?
The Basic rules call out two situations where a Concentration check is required to cast a spell: the caster takes damage and… The spell is Readied but not yet cast (p.72) The spell has a cast time longer than one action (p.79)
What happens if you lose concentration on a spell?
If a creature is concentrating in the spell’s area, the creature must make a successful Constitution saving throw a against your spell save DC or lose concentration. Earthquake (PHB, p. 236) has an explicit influence on concentration if a failed save is made against that spell’s DC. The ground in the area becomes difficult terrain.
What can cause a spell caster to stop concentrating?
A Suggestion or Charm spell, or an effect similar to those spells, could induce a caster to stop concentrating in a spell. Out of combat, something like a bribe or a persuasion attempt, or an intimidation attempt, could do similarly.
Can a grappled condition break a spellcaster’s concentration?
As you noted in your question, the Grappled condition does not break concentration. But, if a character with the Grappler feat (PHB p. 167) and the Mage Slayer feat (PHB p. 168) grapples the caster in question, an interesting synergy arises:
