Put a +1/+1 counter on target creature, then put a +1/+1 counter on each creature you control with a +1/+1 counter on it.
The state-based action that removes matching +1/+1 and -1/-1 counters wonâ€™t check until after Lifecrafterâ€™s Gift finishes resolving. Itâ€™s possible put a +1/+1 counter on a creature with a -1/-1 counter on it and then give it a second +1/+1 counter.
The target creature will receive a second +1/+1 counter shortly after the first.
If there is a +1/+1 counter on a noncreature permanent you control, such as a Vehicle that isnâ€™t crewed, it wonâ€™t get another one from Lifecrafterâ€™s Gift.
If the target creature becomes an illegal target, Lifecrafterâ€™s Gift doesnâ€™t resolve and none of its effects happen. You wonâ€™t put any counters on other creatures.