2023-04-14 : If a spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell’s total cost. For example, if a spell’s mana cost is {X}{R} and your opponents have drawn two cards this turn, you could choose 5 as the value of X and pay {3}{R} to cast the spell.

2023-04-14 : If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben’s ability), apply those increases before applying cost reductions.

2023-04-14 : That ability can’t reduce the amount of colored mana you pay for a spell. It reduces only the generic mana component of that cost.

2023-04-14 : The cost reduction can apply to alternative costs such as flashback costs.

2023-04-14 : The last ability of Heliod, the Warped Eclipse doesn’t change the mana cost or mana value of any spell. It changes only the total cost you pay.

2023-04-14 : The “as though they had flash” effect applies only to casting spells. It does not, for example, change when you may activate abilities that can be activated “only as a sorcery.”