Banjo crouches down while Kazooie deploys an explosive Grenade Egg backwards. The egg bounces in a slightly unpredictable fashion before detonating on contact or on a timer. As an item, it can be picked up by any player, though this does not stop it from exploding in characters' hands. However, this property makes the move useful for bomb recovery. Only one Grenade Egg can be present at a time; Kazooie refuses to use another until the first has exploded.
The manner in which the egg is deployed originates from Banjo-Kazooie, which can be performed after the duo learns how to fire eggs. If the player holds Z while pressing the up C button, eggs will be fired normally from Kazooie's mouth in a straight line. But if the player presses the down C button instead, Kazooie lays the egg behind Banjo, which bounces away along the ground. Eggs fired this way bounce slowly and with much variance based on terrain slope, making its utility very situational.
Banjo-Tooie introduces different types of eggs aside from the standard Blue Eggs; Grenade Eggs are the third egg type. They explode instead of simply breaking on impact or distance expiry, dealing high damage and destroying many sorts of objects, but also hurt Kazooie if they explode too close. Kazooie can carry only 25 of them (though Cheato can double this limit). Grenade Eggs can only be fired one at a time and are mandatory for defeating several enemies and bosses. In the multiplayer first-person shooter mode, Grenade Eggs deal 4 damage (out of most characters' 8 health) and can cause friendly fire.