Currently, the tiamat tag is housing a few different characters by different people. On top of that, there's several other tiamat* character tags and a couple artist tags also. I think that warrants disambiguating tiamat since there's no clear indication who it's intended to refer to.

Relating to a particular Tiamat character, specifically from D&D, I notice most of their posts are being put under tiamat_(god). However, that tag is for a "Babylonian god, often depicted as a sea serpent or dragon, and generally considered a symbol of chaos." While I wouldn't doubt D&D lifted the basis for their Tiamat character from this, I would think the D&D depiction should have its own tag. The wiki even notes, "Dungeons_&_Dragons contributed to the multi head depiction often seen nowadays," indicating the multi-color multi-head depiction is from D&D rather than of the mythological god.

Finally, it would also make sense to Implicate tiamat_(god) -> babylonian_mythology, once the D&D depictions have been moved to its own tag, given that's what the god tag is supposed to be for.