Unstable Shapeshifter seems to no longer copy creatures if two of them are on the board at once. The game also freezes if you end the turn while two of them are on the board.
Give the Tempering, Ricochet, Ricochet, Titan, Fractal the Tempering, play all Temperings on your Titan, and have a SoR'd or previously quinted Crusader endow the super-Titan for 201-261 damage.
Spoiler for Hidden:
Assemble the OTK:
Fractal the Tempering:
Press the Button:
The draw engine is of course Sundial/Regrade/Scattering Wind, which works wonders in OTK decks. Explosion is to destroy the opponent's weapon if necessary. I currently run a three-Sanctuary/Mirror Shield/Flying Weapon variant for arena, but that's only to counter the current decks; it works worse in general.
Mulligan for Novas, but try not to discard anything on the first turn if you're going second. Normally you use Scattering Wind if your hand is full of combo pieces and Sundials/Regrades while you already have a sundial up (or to search for more Sundials and Regrades when you've run out), but using it to rush through the deck for a specific counter like Sanctuary can also be viable.
As with all OTKs, it's vulnerable to mill and to discard/quanta control before it puts up a Sanctuary. It also does poorly if a Sundial gets blown up during a critical turn or if a Trident/Earthquake deck hits all the Fire Pendulums.
There's not much practical reason to use this particular OTK instead of something like House of Mirrors or whatever vanilla OTK fits your preferences, but who's never wished to be able to fractal a spell at least once? (Besides, constantly instant-losing to the deck in the screenshot because it runs Broken Mirrors quickly became irritating.)
I tried to test out a Ricochet/Cremation/Black Cat deck when I found out that playing Cremation on a Black Cat freezes the game. Also, if you play Cremation on another creature and it ricochets to a Black Cat, it doesn't freeze the game, but the game lets you use that Cremation again.
EDIT: Ricochet'd Cremations also just kill the Black Cat without regard for its multiple lives.