Tiamats Hex*

As you place a curse on a creature that you can see within range, the creature has five orbs orbit it head.  Until the spell ends, you deal an extra 2d6 chromatic damage to the target whenever you hit it with an attack.  Choose one of the d8's,  the number rolled on that die determines the attacks damage type, as shown below.
d6 / Damage Type
1 / Acid  
2 / Cold 
3 / Fire  
4 / Lightning  
5 / Poison
6 / Choice

The target also has disadvantage on ability checks made with a chosen ability.

If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to curse a new creature.

At Higher Levels. When you cast this spell using a spell slot of 3rd or 4th level, you can maintain your concentration on the spell for up to 8 hours. When you use a spell slot of 5th level or higher, you can maintain your concentration on the spell for up to 24 hours.