what monsters can you meta into Blue-Eyes Ultimate Dragon?

There aren't any are there?

Blue-Eyes Ultimate Dragon is level twelve, and as far as I can remember there are no other level twelve monsters in the TCG right now.

.....................none.........................only 3 Level 12 monster's exist in the game.........

Blue-Eyes Ultimate Dragon
Master of Dragon Knight (japanese)
Five God Dragon (japanese)

in which case....Master of Dragon Knight and Five God Dragon are stronger, but are also Fusion Summon only....

The closest you'll find is Gate Guardian, which is level 11 and the various level 10's....and there's no card that increases level's at all either....

I think you can use the dragon mirror on 5 random dragons in your graveyard to fusion summon F.G.D. Then metamorph the lv 12 f.G.d into blue eyes ultimate if you want. but why would you?

cyber stein seems like the best use for ultimate. I've seen conventional fusion with ultimate fail even with the dragon mirror. because it's so rediculously hard to draw all three blue eyes and a fusion card. deck thinning with thunder dragon. T.A.D.P.O.L.E. nimble nomunga, toon table of contents. etc. may be your best attempt. at conventional fusion. but that dedicates alot of your deck for that simple purpose. cyber stein therefore for 5000 lp is rather cheap summoning of blue eyes ultimate compared to retiering your entire deck to pull it.

even kaiba used giant germ with some reason behind it.

Kaiba was always one of getting powerful monsters onto the field quickly...Giant Germ...Kaiser Seahorse...Cost Down...Clone Duplication...etc...that way he has either no tributes needed for the tribute or has monster's tribute for them