Glamdring
Legendary Artifact — Equipment
Equipped creature has first strike and gets +1/+0 for each instant and sorcery card in your graveyard.
Whenever equipped creature deals combat damage to a player, you may cast an instant or sorcery spell from your hand with mana value less than or equal to that damage without paying its mana cost.
Equip 
Andrea Piparo
Rulings
If you cast a spell using Glamdring's triggered ability, you do so as part of the resolution of the ability. You can't wait to cast the spell later in the turn. Timing permissions based on the card's type are ignored.
(wotc • 2023-06-16)
If you cast a spell "without paying its mana cost", you can't choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
(wotc • 2023-06-16)
If the spell has {X} in its mana cost, you must choose 0 as the value of X.
(wotc • 2023-06-16)
Printings
Rulings
If you cast a spell using Glamdring's triggered ability, you do so as part of the resolution of the ability. You can't wait to cast the spell later in the turn. Timing permissions based on the card's type are ignored.
(wotc • 2023-06-16)
If you cast a spell "without paying its mana cost", you can't choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
(wotc • 2023-06-16)
If the spell has {X} in its mana cost, you must choose 0 as the value of X.
(wotc • 2023-06-16)