Add to your card pool with black cards, first released in ST-05, and yellow cards, first released in ST-07
Grim Flayer, Glowspore Shaman, and Meren of Clan Nel Toth all work towards either filling up the graveyard or using the graveyard as a resource, as well as playing nicely with a lot of the fun buildarounds in that color pair like Birthing Pod and Recurring Nightmare
Every Card In The Amber & Amethyst Disney Lorcana Starter Deck Ursula's Return Set Amber and Amethyst was a combination that was already seen as a starter deck in The First Chapter , but bringing it back for Ursula's Return has an entirely different flavor
Generally only viable in super-aggressive decks because this wont often make your creatures win combat, it often can just turn a blanked creature into a trade but doesnt enable you to push through damage
Finally, one of the most famous Shapeshifters is Mirror Entity, which can threaten a lot of damage