Castigation

When you or another creature you see within range are successfully targeted with a (single-target) spell, Castigation can be cast as a reaction to attempt to redirect the spell away from the original target and towards a new single target of your choice.  This spell has two separate effects (attempting to direct the spell away from its target, then attempting to assign a new target).

If the targeted spell is 5th level or lower, you automatically succeed when attempting to force it to miss its target.  If the spell is cast above the level you use to cast Castigation, you must make an ability check (DC 10 + the target spell's level).  A successful ability check results in the original spell missing its target.  The effects (if any) can be directed past the target to hit something behind it (at the DM's discretion).

If the spell is successfully directed away from the intended target, the original caster must make a saving throw, using their spellcasting ability, to prevent you from targeting someone or something new.  The DC for this saving throw is your spellcasting DC.  If the original spell is cast at a higher level than Castigation is cast at, the original caster gets a +1 bonus to their saving throw for each level difference (i.e. casting a 7th level spell vs. a 5th level Castigation would give the original caster +2 on their Saving Throw vs. the redirection).  A failed saving throw results in you choosing a new target, which must be within range of the original spell as if YOU had cast it.  The new target rolls a saving throw as if the original caster had targeted it, using the original caster's DC; if the spell requires an attack roll, you must roll the attack roll against the new target, using any modifiers you would use as if you had cast it.

When you cast this spell using a spell slot of 6th level or higher, the interrupted spell is automatically redirected away from the original target if its level is less than or equal to the level of the spell slot used to cast Castigation.

If you cast Castigation at least one level above the targeted spell, the DC for the original caster's Saving Throw gets +1 for each level difference between the two spells (i.e. casting Castigation as a 7th level spell targeting a 6th level Disintigration gives the DC for this saving throw a +1).