Magical Buster Dragon

[Horu]

The ATK of this card is equal to the number of "Magician" and/or "Buster" monsters in your GY x300. Once per turn, you can banish 1 "Magician" or "Buster" monster from your GY and apply the appropiate effect:

● "Magician": Destroy 1 Spell/Trap card your opponent controls.

● "Buster": Destroy 1 monster your opponent controls and inflict damage equal to its Level/Rank/LINK x500.

[Lone mouse]

Good legacy support for dm and bb also a good idea to banish what gives it attack points for its effect. 

[Sleepy]

This is just broad enough in its archetypical support that it struggles between languages.
-Dark Magician in Japanese is written with symbols that spell the sound ma. ji. sha. n.
-Magician Pendulums from Arc V are written ma. ju. tsu. shi.
-Pikeru and Curran are ma. do. shi.
. . . .I checked instances of Buster and they are fine.... they stanslate to ba. su. ta. regardless of if it is Buster Blader, Cubics, Superheavy Samurai, ABC Dragon, etc.

Have you thought about cropping the image out of that weird frame in the art?

The ATK is..... well for nowadays' standards, it doesn't really matter if it can hit 8000+ or 16,000+ with enough dedication like Gren Maju, Utopia Doble, Rainbow Overdragon, Tyrannno Infinity, etc. It starts up a little cold though... unless you do the equivalent to pre-errata Future Fusion for a few turns straight onto the Buster Blader critters.... you are not using this to hit anything... 

However, the burn is hardcore. Be it a copy of this dragon itself or a "Buster Blader the Dragon Destroyer Swordsman" (which you can drop from the Extra Deck to the GY quick and easy with stuff like Dogmatika cards, some of which don't lock you out of the Extra Deck while doing so)... you are burning 4000 damage, and it is a soft OPT clause. That part sounds like an FTK waiting to happen. Reminds me of Darkstrike Fighter from back in the day where some players considered having 4000 or less LP the same as having 0 LP thanks to the burn.... 

I don't think a hard OPT clause on that would make this fully ok to me but I wouldn't be able to complain about an FTK so at least that's my suggestion there....