You may
exertTo exert a permanent, you choose to have it not untap during your next untap step.
A permanent can be exerted even if it’s not tapped or has already been exerted in a turn. If you exert a permanent more than once before your next untap step, each effect causing it not to untap expires during the same untap step.
An object that isn’t on the battlefield can’t be exerted.
“You may exert [this creature] as it attacks” is an optional cost to attack (see rule 508.1g). Some objects with this static ability have a triggered ability that triggers “when you do” printed in the same paragraph. These abilities are linked. (See rule 607.2h.) (CR 701.43) this creature as it attacks. When you do, it gets +1/+0 and gains
deathtouchDeathtouch is a static ability.
A creature with toughness greater than 0 that’s been dealt damage by a source with deathtouch since the last time state-based actions were checked is destroyed as a state-based action. See rule 704.
Any nonzero amount of combat damage assigned to a creature by a source with deathtouch is considered to be lethal damage for the purposes of determining if excess damage is being dealt.
The deathtouch rules function no matter what zone an object with deathtouch deals damage from.
If an object is no longer in the zone it’s expected to be in as an effect causes it to deal damage, its last known information is used to determine whether it had deathtouch.
Multiple instances of deathtouch on the same object are redundant. (CR 702.2) until end of turn. (An exerted creature won't
untapTo untap a permanent, rotate it back to the upright position from a sideways position. Only tapped permanents can be untapped. (CR 701.26) during your next
untapTo untap a permanent, rotate it back to the upright position from a sideways position. Only tapped permanents can be untapped. (CR 701.26) step.)