Hawk Diesel
Adventurer
Added a lv 15 Invocation! I dunno if it's too strong even at level 15 or if its just gonzo enough for the high level?
Personally, if anything I feel like it's a bit underpowered and a little... bland? Rather than going with the Revivify spell, perhaps something more along these lines:
Rewind Tragedy
Prerequisite: 15th-level Warlock
When danger strikes, you have learned to use your life force to avoid calamity and certain death. When an you or an ally within 30 is reduced to 0 hit points or dies, you can use your reaction to expend your up to half of your hit dice. You then roll the number of hit dice spent, healing the target by the amount rolled. The target of this ability then hums with residual temporal energies, granting them the benefits of the haste spell until the end of their next turn. Once you have used this ability, you cannot do so again until you finish a long rest.
It achieves a similar effect as Revivify, but is a bit more useful given the higher level. The ability also feels like the user is rewinding time.