Mercy could choose to resurrect a target instantly or resurrect herself with the cost of ultimate charge. I’m not sure if 50%, 75%, or 100% charge would be needed to use resurrect. It would still have a 30-second cooldown and cast time if Mercy chooses to not use her ultimate charge.
i dont really think that abilities with an ultimate cost charge would work. it could be a resource ability like moira’s healing but it would work quite weirdly in the game i guess.