It is usually impossible to throw grenades while in Monitor mode. To do so, start Forge mode and in Human mode, aim at your front (close to your foot), then throw a grenade. Before the grenade touches the ground (or before it appears on the screen), press Up to turn into Monitor mode. In Monitor mode, aim at the desired target and quickly tap Up(2). If done correctly, you will throw a grenade while in Monitor mode. When you turn into Monitor mode before the grenade hits the ground, the grenade will be saved so that when you turn back into Human mode it gets thrown again. This is why your player will turn into a human and back into Monitor when you tap Up(2). Note: Spike Grenades will expire if you do not throw it for more than about five to ten seconds. This means that if you tap Up(2), the grenade will not be thrown.