Yidris, Maelstrom Wielder

If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.

If a spell with cascade is countered, the cascade ability will still resolve normally.

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.

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

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.

Spells you cast from your hand this turn will gain cascade even if Yidris leaves the battlefield.

If Yidris's triggered ability resolves more than once in one turn, spells you cast from your hand will gain cascade that many times. Each instance of cascade triggers separately; resolve one cascade trigger and the spell you cast from it before resolving the next cascade trigger.