Centaur
Reference: Centaur
Six limbs without any wings involved — and a second problem the winged creatures do not have: it appears to carry two ribcages, and therefore two sets of lungs.
Scored on every axis
The doubled torso
A centaur is a complete horse with a human torso where the neck should be. Counting limbs gives four legs plus two arms: six, the same violation as the dragon, reached without wings.
The structure also implies two thoracic cavities — the horse’s chest and the human one above it — which means two ribcages, plausibly two sets of lungs, and a circulatory arrangement with no analogue in any vertebrate. The octopus runs three hearts, so multiple pumps are not impossible in principle; but the octopus is built around that from the start rather than having a second chest stacked on a first.
Where the digestive tract begins and ends is left unresolved by the tradition, and this catalogue will not invent an answer it does not have.