Altar of the Lost

This artifact enters tapped.
{T}: Add two mana in any combination of colors. Spend this mana only to cast spells with flashback from a graveyard.

Narset's Reversal

Copy target instant or sorcery spell, then return it to its owner's hand. You may choose new targets for the copy.

Exile target creature you control, then return that card to the battlefield under its owner's control.
Draw a card.

Draw X cards, then discard X cards. Create a 1/1 white Spirit creature token with flying for each card type among cards discarded this way.

Blue spells you cast cost {1} less to cast.

{T}: Add one mana of any color in your commander's color identity.

Spells can't be countered.
Each instant and sorcery card in your graveyard has flashback. The flashback cost is equal to that card's mana cost.