Motion's enemies: the ones who want the river to slow down, settle, and stop. All fan-made fictional characters.
A hulking, slow spirit of silt and stacked stone who believes rivers are "unfinished" until they're dammed, ponded, and useful. Built the dam across the Tine in Arc 2 and commands an army of silt imps. Not evil so much as certain — which, Whit learns, is worse. The dam's fall at the Confluence didn't change Damstone's mind; it just changed the address of the argument.
Fan-made
The quiet one. Stillwater rules a glassy pond where nothing ever happens, and offers Whit the same: rest, peace, an end to rushing. The offer in Arc 3 is genuine, which is what makes it frightening. Stillwater isn't a villain to be beaten but a temptation to be refused — the lore's thesis in spirit form: motion is identity.
Fan-made
Damstone's small, muddy hench-spirits. Individually harmless; collectively, a clog. They stuff side-channels with silt and giggle. Whit's spray bursts are their natural predator. Nobody's favorite characters, including Damstone's.
Fan-made
Whit doesn't fight monsters — Whit fights stillness. Damstone is stillness imposed from outside (the dam); Stillwater is stillness offered as a gift (the pond). The fan lore keeps both around because the question they ask — why keep rushing? — is the question the whole site is trying to answer.