Troll

Big, tough, and green, the Troll is a powerful monster that serves Nemesis in Catacomb 3D.

One of the nastiest early threats, they are green-skinned, black-haired giants equipped with spiked flails.

They reappear in the Catacomb Adventure Series, specifically Catacomb Abyss, where they also take on a new form.

In Catacomb 3D
The Troll is large, and far and away the toughest early monster, being ten times tougher than a Bat and more than 3 times tougher than an Orc, boasting an impressive 10 Hit Points. It is also much stronger offensively, doing roughly twice the damage with each hit. While initially, the player will run into Trolls singly, they will appear in bigger and bigger numbers as the game progresses, and large groups of Trolls are extremely dangerous. Trolls actively try to flank, moving around the player to hit them from the side, which makes them very skilled at surrounding the player. 3 Trolls hammering away can send even a player on Easy difficulty to their doom in short order.

An interesting quirk of this behavior is that a Troll that tries to flank when the player is already cornered (and ergo flanks into a wall) may back off and seemingly run away, only to turn right around and charge at the player once it re-establishes line of sight or takes a hit.

A charged shot followed by a flurry of uncharged shots is the most efficient way to deal with Trolls, though in practice it's often safer to hit them with a barrage of uncharged shots while backing away, counting on the shots' stagger to finish the Troll off before it can get too close. Spells are extremely effective against Trolls as well; a single Bolt can kill three Trolls if they're standing in a row, and due to their size, a Nuke can cut the Hit Points of one in half or more at close range. Players will usually want to reserve their heaviest artillery for emergencies, however.

When killed, the troll pitches forward, bleeding black bile, and it faceplants directly into the floor.

They first appear on the Third Floor and appear in every level until Chaos Corridors.

In Catacomb Abyss
Much rarer, the Troll is one of the tougher enemies still. They first appear in The Battleground of the Titans and are the third-strongest monster in the game. This aside they are fundamentally identical to their Catacomb 3D incarnation.

A much nastier version, the Water Troll, can also be encountered. These fiendish foes have the ability to submerge themselves underwater for ambushes.

There is also a tougher golden version in Catacomb Apocalypse.