Illaoi and those tentacles.

Those aren't real tentacles, they're ethereal. You can literally look right through them, they look ghostly.

So why do they scale with AD and deal physical damage? Shouldn't they scale off of AP and deal magic damage?

It just looks really odd that a ghost-tentacle is treated as if it was a solid mass when its clearly more akin to being a spiritual representation of a part of what ever god she worships.