I have an eldrazi edh deck with Yidris, the maelstrom wielder. What would happen if I came across my Endless One? Would I cast him and he’d become an infinite creature since I casted him for free? And what is his converted mana cost? Would I be able to even cast him?
Sorry if the tag isn’t working this is my first post and I’m not sure I got it right :/
In general, if you cast a card with X in its mana cost due to cascade, the X will be 0; cascade won't let X be anything other than 0 (C.R. 702.84a, 107.3b). (Currently, the only exception is Spoils of War [C.R. 107.3c].) See also this thread.
So then endless one would just be cast onto the field as a 0/0?
You can cast Endless One due to cascade. However, since X will be 0 in your scenario, when Endless One resolves it will enter the battlefield with no +1/+1 counters on it (and go to the graveyard as a state-based action after that, if nothing else is affecting Endless One's toughness) (C.R. 608.3, 117.3b, 117.5, 704.5f).