Rulings

• You must already control a Mountain as Arena of Glory enters the battlefield for it to enter untapped. If it enters the battlefield at the same time as a Mountain when you control no other Mountains, it will enter tapped.2024-06-07
• If an exerted permanent is already untapped during your next untap step (most likely because an effect untapped it), exert's effect preventing it from untapping expires without having done anything.2024-06-07
• If you gain control of another player's permanent until end of turn and exert it, and then that player regains control of it, it will untap during that player's untap step.2024-06-07
• The mana generated with Arena of Glory's last ability can be spent on anything, not just creature spells.2024-06-07
• If the mana generated with Arena of Glory's last ability is spent on two different creature spells, each of those spells (and resulting creatures) will gain haste until end of turn.2024-06-07
• If mana generated with Arena of Glory's last ability is spent to pay any part of a creature spell's cost, including an alternative or additional cost, that creature spell (and the resulting creature) will gain haste until end of turn.2024-06-07
• If mana generated with Arena of Glory's last ability is spent to cast a noncreature spell that creates tokens, those tokens won't gain haste.2024-06-07
• If mana generated with Arena of Glory's last ability is spent on a noncreature spell that becomes a creature later in the turn, that creature won't have haste.2024-06-07