I kill plants. xD All the water wisteria I bought a few weeks ago ended up dead and my moneywort isn't doing too well, either. I've been looking for hornwort or java moss, because I hear those are impossible to kill but no one near me sells it.
Though shrimp might be fun. I tried to put one in my 5.5 gallon tank with Beethoven, but the big bully killed the shrimp immediately. He didn't even want to eat it. I just found him hovering over the dead shrimp, staring at it like he was daring it to move one more time. xD Apparently there will be no tank mates for Beethoven.