Whispersteel Dagger
Artifact — Equipment
Equipped creature gets +2/+0.
Whenever equipped creature deals combat damage to a player, you may cast a creature spell from that player's graveyard this turn, and you may spend mana as though it were mana of any color to cast that spell.
Equip 
Svetlin Velinov
Rulings
You don’t choose a card to cast as Whispersteel Dagger’s ability resolves. You simply get a permission to cast one later.
(wotc • 2020-09-25)
You’ll still pay all costs for a spell cast this way, including additional costs. You may also pay alternative costs if any are available.
(wotc • 2020-09-25)
In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, any spells and/or permanents you control from Whispersteel Dagger’s ability are exiled.
(wotc • 2020-09-25)
You must follow the normal timing permissions and restrictions for the spell you wish to cast.
(wotc • 2020-09-25)
Rulings
You don’t choose a card to cast as Whispersteel Dagger’s ability resolves. You simply get a permission to cast one later.
(wotc • 2020-09-25)
You’ll still pay all costs for a spell cast this way, including additional costs. You may also pay alternative costs if any are available.
(wotc • 2020-09-25)
In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, any spells and/or permanents you control from Whispersteel Dagger’s ability are exiled.
(wotc • 2020-09-25)
You must follow the normal timing permissions and restrictions for the spell you wish to cast.
(wotc • 2020-09-25)