Slayer Of Terramorphous is a LegendaryClass Mod for all classes manufactured by Dahl, Jakobs, Maliwan, and Bandit. All classes of Slayer of Terramorphous class mods can be obtained as a guaranteed drop from Terramorphous the Invincible.
The drop rate of "Slayer of Terramorphous" is 100%, but which class the mod applies to is random.
Zer0's "Slayer of Terramorphous" was fixed in a recent "hot fix", previously being bugged, supporting Inconceivable (one of Salvador's skills) instead of Fast Hands, resulting in only 4 bonus effects instead of 5.
The design on the Gunzerker's version is from the skill "Berserk" from Brick's skill tree.
The design on the Siren's version can be seen both as a part of the art used for Lilith's skill "Phasewalk" and as the icon of her action skill.
The design on the Mechromancer's version is a cartoon styled version of Claptrap.