Honestly i find it that for the level 3 only thing it gains is wall hack and double damage is underwhelming. 4.5 second for only a double boost is... well underwhelming. But its not just that even if its infinitly piercing and wall hacking i think it could have more.
What i had in mind was something i was already thinking: Instead of just being a beam, it'd look like the orbs that the true eyes of cthulhu throw at you in an hexagon formation, and well do what the rest said, infinitly piercing, wall hacking, but at the same time being extrmely hard to avoid and actual exploding after 200 blocks or piercing 10 enemies. It deals, again, double the damage the sword would do and the explosion would do the same thing and have a big blast radius.
Altough honestly that was my idea for a sword of my own but i dont really mind posting it here. I'd call it Seventh Heaven simply because im a digimon fanatic.