Its a token-making machine in the right decks, and can enable itself with a strong activated ability
The only cards of competitive value are Ponyta, Rapidash, and Magmar, from the tutorial deck, which all see play in Blaine decks.
(4/8/2016) Some delirium abilities that appear on instants and sorceries use the word "instead." These spells have an upgraded effect when they resolve if there are four or more card types among cards in your graveyard
There's no once per turn clause here, and eerie even triggers off unlocking rooms, if you're so inclined
This fits in quite well, allowing me to "Nefarious Archfiend Eater of Nefariousness" to build a Rank 8, or use "El Shaddoll Shekhinaga" to trigger "Machina Kernel" in the Graveyard
But fyi, Rotting Rats is a zombie, which matters to some of you