I don't know, this is very chaotic...
If i understood well, the lightining does 1 damage and then jumps to a new target (chosen from ONLY opponent creatures + the opponent itself)
Let's suppose the opponent has 1 massive dragons in play, at full 30 hp.
Arc Lightning deals 1 damage to the dragon, then do a random jump. Since there is only 1 valid target, it will choose the opponent.
It gives 1 damage to the new target and then do another jump. Then it will choose the dragon again.
So, if the dragon has 30hp and the player has less hp than the dragon (like 29 HP), sure the opponent will die!
Let's use 2 Basilisk Blood on a photon: you can kill an opponent with 40HP.
Unless i misunderstood the mechanic, this is definitely OP.