Counteraction

You attempt to interrupt a creature in the process of performing an activity. make an ability check using your spellcasting ability. The DC equals 10 + the target's level (or CR if the target has no level) - your level (or CR if you have no level). On a success, the creature's action fails and has no effect.

For the purposes of the reaction of this spell, "an action" excludes a bonus action, interact with object or reaction. Therefore, you could counter the bandit king attempting to use their multiattack, but not if they were attempting to use misty step.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the base DC for this spell is reduced by 1 per spell level above the 5th.