This is just a low level player facing kru. All the comments about getting better mods, etc. are really irrelevant at low level. To the OP: there are certain characters, like KRU, that will be extremely hard for you to kill at the beginning because you lack the tools needed in the early game. As you level up, get more characters, better synergy, etc. it will become easier and easier to the point you’ll look back at this and get a chuckle. It’s painful now, but won’t be for long. The reason you’re having trouble now is because he gets healed every time you hit him and you’re just lacking the damage to counter how much he’s healing. It won’t be that way forever.