So THAT'S it!
Overall, I'm pleased to say that I am happy with Incubus Pulsum. It's very fun, very well made, and I absolutely LOVE the video game motif in the music! Metropolis Zone forever! However, I think I've figured out why this game is so "difficult": oftentimes, the lag time between when you press the button and when the mallet actually hits is sometimes atrociosly long. There were honestly times when the mallet would fall half a second after I pressed A. And in cases where you must press up and down simultaneously, fuhgeddaboutit: the mallet simply doesn't work in that case. Also, as someone else previously mentioned, the corner monsters really throw off your timing since they appear before the others.
So yeah, work on the timing issues a bit, and you'll have yourself a bit of genius here. I'm almost as much in love with this as I am Ongaku.
(P.S. I loved you guys' submissions to Four Second Firestorm!)