At one point, he and Maze hatched a plan to kill Amenadiel that went awry; instead, Charlotte died in Amenadiel’s place.
Chloe was eventually clued in to all of the stuff Lucifer had been telling her about being the Devil over Lucifer’s three seasons on the air.
Over the last few episodes, the big storyline had been about Pierce trying to figure out how to die, and then deciding that was a bad idea, instead trying to live a good life with Chloe.
In the meantime, Chloe, Lucifer and Dan figured out that Pierce was involved in Charlotte’s death, leading to a confrontation where Pierce tried to attack Lucifer and ended up dying, instead.