Creature â Naga Druid
: Add one mana of any color.
, Exert Oasis Ritualist: Add two mana of any one color. (An exerted creature won't untap during your next untap step.)
Some cards in the Hour of Devastation set let you exert a creature as a cost to activate one of its abilities. You can exert it to pay that cost even if youâ€™ve already exerted it earlier in the turn. Exerting it multiple times will keep it tapped only during your next untap step.
You canâ€™t exert a creature unless an effect allows you to do so. Similar effects that â€œtap and freezeâ€ a creature (such as that of Decision Paralysis) donâ€™t exert that creature.
If you gain control of another playerâ€™s creature until end of turn and exert it, it will untap during that playerâ€™s untap step.
If an exerted creature is already untapped during your next untap step (most likely because it had vigilance or an effect untapped it), exertâ€™s effect preventing it from untapping expires without having done anything.