Having a way to consistently sacrifice the Warden is the key to making it amazing, so it will be strongest in decks with a heavy sacrifice theme like Athreos, God of Passage, Karador, Ghost Chieftain, and Teysa, Orzhov Scion
If From Under the Floorboards's madness cost was paid, instead create X of those tokens and you gain X life
The following two chapters can help you do some serious damage and clear the board while allowing you to keep your Phyrexians
In a mono-color deck, it's impossible to be color screwed (assuming you're not playing an absurd amount of colorless lands for some reason), and in a two-color deck, it's pretty unlikely that you'll get color screwed with a properly built mana base featuring a reasonable number of dual lands and other types of ramp / fixing
Charge Search your deck for a Basic [Electric] Energy and attach it to this Pokemon