Voidslime

Simic Combine Spell
Level 3
Casting Time: Instantaneous
Range: 80 ft
You attempt to interrupt a creature in the process of Casting a Spell, using a Class Ability (such as Action Surge, or a Paladin's Smite, or a Barbarian Rage), or activating an Item's Ability.
If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.
If you are attempting to interrupt a creature's Class or Item Ability, they roll a Dexterity (?) Saving Throw. On a fail this spell consumes the activation of that ability but no effect is produced.
At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the interrupted spell has no effect if its level is less than or equal to the level of the spell slot you used.