Apex Devastator

Each of Apex Devastator's four cascade abilities will look for a nonland card with mana value less than 10 (Apex Devastator's mana value). This doesn't change even if one or more of the spells you cast because of those cascade abilities has cascade itself. Each of those additional cascade abilities, if any, will refer to the mana value of the spell that caused it to trigger. In other words, each cascade ability cares only about the spell that caused it to trigger, the stack can get messy, and we wish you luck.

Each instance of cascade triggers and resolves separately. The spell you cast due to the first cascade ability will go on the stack on top of the second, third, and fourth cascade abilities. That spell will resolve before you exile cards for the second cascade ability. The spell you cast for the second will resolve before you exile cards for the third, and so on.

When the cascade ability resolves, you must exile cards. The only optional part of the ability is whether or not you cast the last card exiled.