Proliferate (mythic Feat)

you have spent many long hours studying your spells, and meticulously preparing them in such a way that you can bend the properties of those spells to your will.

twice per long rest (as a bonus action) you may choose to double the duration of a buff or debuff. this additionally causes any friendly creature affected by this ability to automatically succeed their next saving throw, and any hostile creature affected by proliferate to fail their next saving throw. 

DM note: mythic feats are created with the knowledge that these feats are very powerful and should only be given to players at a DM's discretion. Also great for dmpc bosses or bbegs'!