Arena of Glory (PMH3 215s)

Land • Modern Horizons 3 Promos • Rare

This land enters tapped unless you control a Mountain.
{T}: Add {R}.
{R}, {T}, Exert this land: Add {R}{R}. If 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.)

Illustrated by Jorge Jacinto.