Rootha, Mastering the Moment

• WWizards of the Coast2026-03-20
  Official Ruling
  A spell's mana value is determined only by its mana cost. Ignore any alternative costs, additional costs, cost increases, or cost reductions.
• WWizards of the Coast2026-03-20
  Official Ruling
  For spells you cast with in their mana costs, use the value chosen for X to determine the spell's mana value.
• WWizards of the Coast2026-03-20
  Official Ruling
  Rootha's ability will check as your beginning of combat step starts to see if you've cast an instant or sorcery spell this turn. If you haven't, the ability won't trigger at all. It's not possible to cast an instant or sorcery spell during your beginning of combat step in time to have the ability trigger.

Rulings via Scryfall