Jarmes Asylum Room

Jarme spent his last days of life covering the walls of his cell with drawings, etched with a cast-off lump of charcoal. The resulting images were unsettling, to say the least.
They are multiple depictions of a tentacled creature something like a squid or octopus, but determining further details is difficult, however there are some elements that can be determined:
The specific elements include the following details:
The tentacled creature is shown devouring a coastal city whose skyline suggests the Styes. The creature is shown trapped in a deep chasm or underwater pit, its tentacles wrapped around humanoids who are dragged down into the inky dark. The tentacled creature appears to be shackled by a collar attached to a chain, with the chain held by another creature resembling a vile, multi-tailed fish. The creature is recognized the as an aboleth.