TARDIS

You may planeswalk at the time TARDIS's triggered ability resolves, not at the time you cast the next spell.

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.

Cascade triggers when you cast the spell, meaning that it resolves before that spell. If you end up casting the exiled card, it will go on the stack above the spell with cascade.

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

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.

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.

A spell's mana value is determined only by its mana cost. Ignore any alternative costs, additional costs, cost increases, or cost reductions.

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