Falemirous, the guy who's been really helping with the Miiverse Project, has made a really awesome Krystal mod for Half Life 2! The mod replaces Alyx, the secondary companion character, with Krystal. As a result, you will have the pleasure of Krystal guiding you through part of the game's tutorial, and you will see her in other places throughout the rest of the game. Though the rig is a bit unorthodox, it's hard to argue with the results. It features facial animation, a physically active tail, and various "jiggle bones" to make for a very dynamic character. The EMP tool is replaced by Krystal's Staff. Depending on which version you get, Krystal can either fire a blaster or a mini gatling gun. Both the guns and the Staff use sound effects from their respective games.
The mod is compatible with Half-Life 2, Half-Life 2: Episode 1, Half-Life 2: Episode 2, and Synergy (a free multiplayer Half-Life 2 mod). You can download either the blaster or gatling gun versions from the new Falemirous Half Life 2 Alyx Mod page.