Concentrate spell

You can use your turn to power up your next spell. 

You spend your action and bonus action concentrating your power, and putting that into your next spell, dealing 1d4 extra damage, per spell level. So if you use a cantrip or a 1st level spell you do 1d4 extra damage. If you use a 2nd level spell you get 2d4 extra damage and so on.

If you get hit while waiting to use the spell, you will have to do a wisdom saving throw DC = damage (max 40) - 3 + attackers intelligence modifier

This ability can be stacked, by using multiple turns in concentration. And then adding the same amount, to the attack.

While the concentration is active you, your armor class is decreased by 2