Contest

You can try to interrupt a creature casting a spell with a casting time of an action or bonus action. To do this, both you and the creature make a Contested Counterspell check, using this formula:

Contested Counterspell check = 1d20 + 2 × spell level + spell attack modifier.

• If you fail, the creature’s spell succeeds. You take 1d6 psychic damage for each level difference between the spells used.
• If you succeed, the creature’s spell fails. The creature takes 1d6 psychic damage for each level difference between the spells used.
• If there's a tie, the spell fails, and both of you roll on the Wild Magic Surge table.

If another creature tries to join the Contest, they can give one of the original casters advantage instead of rolling themselves.