Urza, Lord High Artificer
Legendary Creature — Human Artificer
When Urza, Lord High Artificer enters the battlefield, create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control."
Tap an untapped artifact you control: Add .
: Shuffle your library, then exile the top card. Until end of turn, you may play that card without paying its mana cost.
イラスト：
Modern Horizons 1 Timeshifts#11神話レア英語適正
裁定
Urza’s last ability doesn’t change when you can play the exiled card. For example, if you exile a sorcery card, you can cast it only during your main phase when the stack is empty. If you exile a land card, you can play it only during your main phase and only if you have an available land play remaining.
If a spell has 
in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
The token created by Urza’s first ability will count itself, so it’ll be at least 1/1.
You can tap any untapped artifact you control, including an artifact creature you haven’t controlled continuously since the beginning of your most recent turn, to pay the cost of Urza’s mana ability. Tapping an Equipment this way won’t affect its abilities or the equipped creature.
If you don’t play the card exiled with Urza’s last ability, it remains in exile.
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 (such as that of Lesser Masticore), you must pay those to cast the card.