4 Mallets is what malleteers that are more experienced do to become better at being a pit performer. It's pretty self-explanatory. The performer simply holds 2 mallets in each hand.
Sike, it's not simple at all, but it is fun. When you start, you constantly face the threat of a mallet flying out of your hands and across the room because your hands are too sweaty. The more you play with them, the bigger the calluses get on your middle finger. Your hand also gets fucking ripped, especially in your thumb.
But most importantly of all, your music actually sounds good.
Man, I wish I could play 4 mallets like Timmy can. Look at his wrists fly!