Dy-No-Mite is a decently balanced character with a grenade launcher as a starting weapon.
Since he uses bombs as his main weapon, it is important to keep your distance from your projectiles. Keep in mind that bombs will arc in the air and roll on the ground unless you have certain items. When dealing with enemies that chase you, shooting a little bit ahead of you on the ground may let the bomb kill the persuer while still letting you avoid the blast.
If you switch to your katana whilst reloading, and switch back, the grenade launcher will be ready to fire. This can cause mayhem if you can do it fast enough.