There are 20 different playable Spelunkers available in Spelunky HD that can be used in all single player and multiplayer game modes.
Each of the Spelunkers have identical abilities; the differences between them are purely cosmetic and do not affect gameplay.
Four are available from the beginning, but the remaining sixteen must be unlocked by fulfilling certain requirements.
Unlocking all 16 secret characters earns the Achievement 'The Entire Gang'.
A padlock in the character selection menu tells you how many Spelunkers remains to be unlocked.
In the Playstation 3 port, The Eskimo, The Round Girl, The Round Boy, The Ninja, The Cyclops, The Viking, The Robot, And The Golden Monk all come free with purchase of the game.This means that you no longer need to purchase The Cyclops from the Black Market for $10,000.
The Cyclops is based on the titular character of What is bothering Carl? an interactive storybook created by Spelunky's lead programmer Andy Hull. This is referenced in the pop-up prompt to purchase the character when he appears in the Black Market, which reads 'Bother Carl'.
The Ninja may be a reference to Reptile from Mortal Kombat. In the original Mortal Kombat Reptile was a hidden character who could be found on the stage 'The Pit'. Normally the characters would fight on a bridge over the top of the pit and could knock each other off to spikes below for a grisly demise, but you couldn't reach the actual pit itself. However if you managed to get a two flawless rounds in a row on that stage, and finish with a Fatility then you could reach the floor of the pit and fight Reptile himself. While it may be a coincidence, both characters are green, are ninjas and can be found by descending into a pit of some sort.