Callisto is a level 470 bear that can be found inside Callisto's Den. He is killed for the valuable voidwaker hilt, claws of callisto, tyrannical ring, and Callisto cub, though he can also drop the dragon 2h sword and dragon pickaxe.

Warning: Like all Wilderness bosses, Callisto resides in a multi-way area and in moderately high-level Wilderness. You may be attacked at any time during the kill. Do not bring any items that you are not willing to lose.

Callisto can deal incredibly high melee damage through prayer, so melee combat is not advised. Callisto is also immune to magic damage, so ranged is the ideal method for doing damage. However, the boss will approach targets constantly, so a method of freezing the boss in place is strongly recommended outside of the largest of groups. Spells such as Ice Barrage or Entangle are commonly used. Spells such as Vulnerability, (especially when combined with the Tome of water effect), or even a dragon warhammer are sometimes also used to lower its defence. A charged Webweaver bow has a powerful bonus against Wilderness monsters and can provide the fastest kills, but it carries higher risk compared to other setups. Players (especially Ironmen) who do not have access to the above weapons commonly use a rune crossbow with broad or Ruby bolts (e) in a group for effective damage.

Callisto has the lowest defence against ranged and is particularly dangerous when up close. The ideal setup is 3-4 items to maximize ranged strength and accuracy, along with magical defence and tank equipment, such as a Dinh's bulwark, for PK'ers. In a team, consider having 1 group member equipped with a charged tome of water and runes to cast vulnerability to reduce Callisto's defence by 15% on a successful hit, increasing the group's DPS by around 5-7% depending on gear.

Callisto will spawn to the south of the den, right in front of the exit leading into the Escape Caves. If you wish to avoid player killers, it is recommended to place a secondary account waiting outside the entrance to scout potential threats. All players who enter the den will spawn to the north, similar to Venenatis' lair.

Callisto uses highly damaging melee attacks and is weakest to ranged attacks. Due to hitting much harder, players are recommended to range him. While he is immune to magic damage, ice spells will almost always land, binding him temporarily. If he cannot attack with melee, he will begin using a much weaker ranged attack until he can reach his target. Callisto will occasionally launch a white orb at his target, of which they should switch on Protect from Magic or risk taking up to 50 damage from the attack.

Upon reaching 66 and 33% of his health, Callisto will roar, launching bear traps all across the arena. Stepping on one will deal up to 15 damage and bind the player for a few seconds. The traps will linger around for a short duration before expiring, but will immediately be replaced with a fresh set of traps. While roaring, he will also glow red, breaking free of binds in the process and requiring a player to refreeze him.

If bringing low risk items, it is recommended that rather than trying to leave via the Escape Caves to rebank, the player instead suicide to Callisto, as they will be able to reclaim items for free as apart from the rares (which should be covered via Protect Item) as none of the drops are individually over 100,000 coins. The player will lose untradeable items such as looting bags however.