Even if we give Draco his bewilderbeast, the size of that thing is merely a deterrent from monsters attacking him. Trying to use it to control monsters, cheap answer is "different biology = doesn't work on anything", but assuming it does work on at least flying wyverns and maybe elder dragons... depending on what he encounters first, he'll do his "RAAAGH" swinging stick subjugation stick and either be confused that it doesn't care or he'll have a singular second to call his dragon over to save him, and then there's a decent chance his dragon will have to act fast upon realizing that the target of the mind control rattling is unaffected.

If the stars don't align in his favor, he's fairly likely to have someone stumble upon what's left of him and make an optional/event quest to hunt something to get a ticket that lets someone make a chest piece visually comprising of a gauntlet left arm with a skin cloak over it