Eligible enemies are indicated by the Hunter's Grenade icon above their heads.
Throwing the Hunter's Grenade at an eligible enemy will cause it to despawn from the player's inventory, as well as dropping a Blueprint Extractor nearby. The spawned Elite does not carry any special abilities, unlike normal Elites.
If all blueprints from the enemy type have already been acquired, the enemy is a boss, already is an Elite, or the player misses, the Hunter's Grenade will drop harmlessly to the ground and turn into its item form. For example, Zombies at 0 BSC will not drop the Bobby Outfit, and if the player has all other blueprints that can be obtained at 0 BSC, the Hunter's Grenade will not work. The game will simply say "No new blueprints can be obtained from this creature".
If an eligible enemy has no Elite variant (Kamikazes, Impalers, Bats, Protectors......etc), the grenade will instead transform it into a standard Elite Zombie. The extracted blueprint will still be from the original enemy's loot pool.
Elites spawned by this skill will count towards the "Not so Tough" achievement when defeated, either with weapons or the Blueprint Extractor.
If the Hunter's Grenade misses, it will only transform back into its item form when the projectile has landed. For example, if it somehow falls into lava at Cavern, the grenade will just despawn and a new copy does not appear.
The Hunter's Grenade is unlocked from the Collector through the Specialist's Showroom upgrade. Once unlocked, it always appears in the Prisoners' Quarters behind a gold door within the Specialist's Shop, which can be unlocked for 3000 gold, or destroyed for a 50-kill curse.
Cannot be used to feed Diverse Deck Electrodynamics.
Trivia
Although the Hunter's Grenade scales with Brutality, it lacks any meaningful scaling effects.
The Hunter's Grenade references a Poké Ball, a spherical device used to capture Pokémon in the well-known Pokémon franchise.
The description of the item is a reference to the franchise's "Gotta catch'em all!" slogan.
In early development for the Baguette Update, the Hunter's Grenade was instead named "Pokebomb".
When the Grenade-spawned Elite is below 40% health, the grenade's miniature icon (which resembles a Poké Ball) appears over them.
The fact that the Elite must be weakened before using the Blueprint Extractor might be a reference to the capture mechanic in the video games, where the chances of capturing a Pokémon increase as their health decreases.