Aliasing multiple_legs -> extra_legs.

Reason: "Legs" by definition is multiple.

Agreed. Multiple_legs isn't explicit enough. Technically, a cat with four legs has multiple legs.

Extra_legs implies that something has more legs than the species it belongs to/is based on. e.g. A human with three legs or a centaur with five legs.

The only issue I see is if a creature inherently has fewer legs than normal. I'm not sure if we have any pictures like that, but if there are then we'll also have to introduce some kind of fewer_legs_than_normal tag. We already have the amputee tag for anything that is lacking limbs for unnatural reasons.

Interesting bit: there are no naturally unipedal creatures on Earth.