The dude gets summoned by god with a bunch of people to help another world but when his name's called, someone else steps forward who looks just like him. He's then the last to step forward and god knows he messed up. Instead of getting OP powers, he gets nothing which later manifests as the power of death. He, however, can't use this power as he's an experimentee and right when he escapes, the heroes kill him. He wants revenge so god removes his ability to level up in his next life which he is reborn as a dullahan in, but that's just a demon race where he's reincarnated. Anyways, his new mom dies but he uses his power to control death to keep her soul around.
What you are looking for is named The Death Mage Who Doesn't Want a Fourth Time
Amamiya Hiroto is unlucky. His life consisted of misfortune after misfortune, culminating in an unlucky death during an incident on a school boat trip, trying to save a girl he barely knew. After death, he met a god of reincarnation who requested that the hundred or so dead passengers—one of them being the girl he tried in vain to save—be reincarnated into another world.
Yet a series of unfortunate events forced Hiroto to reincarnate with even less luck than before, starting with nothing but a tremendous amount of Mana. His second life, far worse than his first, came to a cruel end.
However, upon meeting the god a second time, he was informed that there would be yet another reincarnation—one that had already been set in motion and could not be stopped. Not wanting Hiroto to live long, the god cursed him before he was reborn in the hopes that he would either die quickly or commit suicide.
Hiroto was reborn once more as a half Vampire and Dark-Elf being, a Dhampir. Not wanting a fourth life, he is determined to live this third life with the only things remaining from his previous lives—death-attribute magic and his enormous Mana pool.