Arcane Strength

The caster touches a target imbuing the targets body with arcane power, increasing their strength by 1d4+1 and gains advantage on strength checks and saving throws.

At 5th level the target gains 1d6+1 to their strength. At 9th level the target gains 1d6+2 strength and you hit with such force that you score critical hits on a 19 and 20. At 15th level the target gains 2d4+1 and now score a critical hit on a 18,19, and 20.