Epic Soul

You have accomplished a feat of great renown and become an Epic Soul, your reputation precedes you and the realms themselves acknowledge your presence. 

Ability Scor Increase. Increase your Charisma and one ability score of your choice by 1, to a maximum of 20.

Epic Intervention. As an action you turn a number of hit dice into points (these hit dice are expended) and roll 5d4. If the number of hit die points is equal to or greater than the number rolled on the d4s you can describe whatever assistance you seek. The DM chooses the nature of the assistance. If the total hit die points are less than the number rolled on the d4s you fall unconscious and must begin rolling death saves.

If Epic Soul succeeds, you can’t use this feature again for 5d4 days. Otherwise, you can use it again after you finish a long rest.

At 20th level turning all your hit dice into points guarantees success.