In theory, such an ability could go as far as effectively being able to cast any arbitrary spell on zero notice, being the true ultimate in magic versatility. You can't learn and counter his abilities because he can pull new abilities out of thin air at will. Meanwhile, he can perfectly counter whatever you've got the moment he knows about it.
True, Tedd hasn't shown anything beyond analyzing magic, disenchanting himself, and creating devices, and I might be speculating too far, but Tedd himself doesn't know his own abilities and might not have tried to do anything else with magic.