Etherium-Horn Sorcerer

Due to a 2021 rules change to cascade, not only do you stop exiling cards if you exile a nonland card with lesser mana value than the spell with cascade, but the resulting spell you cast must also have lesser mana value. Previously, in cases where a card's mana value differed from the resulting spell, such as with some modal double-faced cards or cards with an Adventure, you could cast a spell with a higher mana value than the exiled card.

The mana value of a split card is determined by the combined mana cost of its two halves. If cascade allows you to cast a split card, you may cast either half but not both halves.

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.

You exile the cards face up. All players will be able to see them.

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Etherium-Horn Sorcerer's first ability can only be activated when it is on the battlefield. If Etherium-Horn Sorcerer isn't on the battlefield when the ability resolves, the ability won't do anything.