I have a character idea for a cleric that idolizes the god of pain.

They focus almost entirely on healing because you can't keep suffering if you're dead, if you're alive you can grow stronger, and therefore, in their own twisted mind, if you're suffering you're growing stronger.

They don't heal people right away unless not doing so would cause them to die and end their suffering. Instead, if the battle is over, they pull out a chart and start asking about how painful the wound is. This can be excruciating for the one who has to sit there and answer questions until they get healed.

The other portion of their build would focus on fighting the undead because they are abominations who cannot feel pain and cannot grow stronger because of it

The god goes along with it because their normal clerics may be into torture, which is great for pain, but they tend to get hunted down because of their extreme methods. This cleric causes pain indirectly by being surrounded by a bunch of murderhobos.