Voorish Sign

You have mastered the Voorish sign, a sigil from an ancient era said to predate the world's creation. Choose a creature that you can see within range. When you would normally roll one or more dice to deal damage to that creature with a spell, don't roll those dice for the damage; instead use the highest number possible for each die. In addition, you can choose a spell of level 5 or lower that you can cast, that has a casting time of an action. You can cast that spell as part of casting Voorish Sign, expending spell slots for both.