Duel Caster

You’ve trained your arcane prowess to a degree where you can multitask, casting new spells while simultaneously holding concentration on old ones.

You gain the following benefits.

Duel Casting: Allows the caster to hold concentration on a previously cast spell in addition to casting another spell of the same level (or lower).

If you do this, roll a concentration check with disadvantage. 

On a successful save, both spells are cast.

On a failed save, both spells fail.