Choose one.

Constitution. advantage on Constitution checks. It also gains 2d6 temp hit points, which are lost when the spell ends.

Strength.  advantage on Strength checks, and theirr carrying capacity doubles.

Dexterity. advantage on Dexterity checks. no damage from falling 20 feet or less if it isn't incapacitated.

Charisma.  advantage on Charisma checks.

Intelligence.  advantage on Intelligence checks.

 Wisdom. advantage on Wisdom checks.

For Higher Levels. Using a spell slot of 3rd level or higher, you can target one additional creature for each slot level above 2nd.