Quintorius, Loremaster — ruling 1

You must follow all applicable timing rules for casting the exiled card. For example, if the card is a sorcery card, you can cast it only during your main phase while the stack is empty.

Quintorius, Loremaster — ruling 2

Quintorius's last two abilities are linked. The last ability can target only cards exiled by the triggered ability. If a Spirit you sacrifice to activate the last ability ends up being exiled because of a replacement effect, that card can't be targeted by the last ability.

Quintorius, Loremaster — ruling 3

If the target of Quintorius's triggered ability is an illegal target at the time the ability tries to resolve, the ability won't resolve and none of its effects will happen. You won't create a Spirit token.

Quintorius, Loremaster — ruling 4

If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.

Quintorius, Loremaster — ruling 5

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Quintorius, Loremaster : règles, fonctionnement et interactions (MTG)

Quintorius, Loremaster is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Vigilance At the beginning of your end step, exile target noncreature, nonland card from your graveyard. Create a 3/2 red and white Spirit creature token. , , Sacrifice a Spirit: Choose target card exiled with Quintorius. You may cast that card this turn without paying its mana cost. If that spell would be put into a graveyard, put it on the bottom of its owner's library instead.

How it works : Quintorius, Loremaster

Original English text — Wizards of the Coast / Scryfall

#1April 14, 2023· Wizards of the Coast
You must follow all applicable timing rules for casting the exiled card. For example, if the card is a sorcery card, you can cast it only during your main phase while the stack is empty.
No other card is named in this ruling.
#2April 14, 2023· Wizards of the Coast
Quintorius's last two abilities are linked. The last ability can target only cards exiled by the triggered ability. If a Spirit you sacrifice to activate the last ability ends up being exiled because of a replacement effect, that card can't be targeted by the last ability.
Card named in this ruling
Spirit
#3April 14, 2023· Wizards of the Coast
If the target of Quintorius's triggered ability is an illegal target at the time the ability tries to resolve, the ability won't resolve and none of its effects will happen. You won't create a Spirit token.
Card named in this ruling
Spirit
#4April 14, 2023· Wizards of the Coast
If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.
No other card is named in this ruling.
#5April 14, 2023· Wizards of the Coast
If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
No other card is named in this ruling.