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/+3 and gains
lifelinkLifelink is a static ability.
Damage dealt by a source with lifelink causes that source’s controller, or its owner if it has no controller, to gain that much life (in addition to any other results that damage causes). See rule 120.3.
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 lifelink.
The lifelink rules function no matter what zone an object with lifelink deals damage from.
If multiple sources with lifelink deal damage at the same time, they cause separate life gain events (see rules 119.9–10).
Multiple instances of lifelink on the same object are redundant. (CR 702.15) 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.)