Arena of Glory is a rare Land card from Modern Horizons 3 (MH3), collector number 351. Current market price: $11.11 (foil $31.62), TCGplayer market prices via Scryfall.
This land enters tapped unless you control a Mountain. {T}: Add {R}. {R}, {T}, Exert this land: Add {R}{R}. If any of that mana is spent on a creature spell, it gains haste until end of turn. (An exerted permanent won't untap during your next untap step.)