Q:How does cascade work with commanders in EDH? For example, if Bloodbraid Elf was your commander, and she dies, would playing her again trigger cascade at 4 converted mana cost or 6?
Bloodbraid couldn’t be your Commander because she isn’t Legendary. There are no Legendary Creatures with Cascade.
That said, you’d only cascade for 3 CMC or less. The Commander “Tax” doesn’t affect the CMC of the spell.