Gacha Club MP Strike and unit list
This Gacha Club active skill is called MP Strike. This ability attacks one enemy and also gives you some MP back at the same time. At lower levels it gives less MP than it uses, but when maxed out you get more MP than the cost of the skill. This skill is really only useful against bosses, and even then, it's usually better to have one unit with MP booster and the other units with better skills. It's not useless though, you can use it effectively if you want to, it's probably not the optimal skill though.
The level progression of MP strike in Gacha Club is as follows:
Level 1: Attack 1 enemy with 2.5x damage and gain 10MP
Level 2: Attack 1 enemy with 3x damage and gain 15MP
Level 3: Attack 1 enemy with 3.5x damage and gain 20MP
Level 4: Attack 1 enemy with 4x damage and gain 25MP
Level 5: Attack 1 enemy with 5x damage and gain 30MP