HorrorClix 1.5 is a term referring to a series of custom content and community-approved additions to the game originating from It's Wicked Fun, and the play format that allows that content to be used.
In 2008, near the release of Nightmares, a leaked WizKids Powerpoint presentation stated that Nightmares would be the final HorrorClix booster set and that future Action Packs would depend on the sales of the Freddy vs. Jason Action Pack. However, aside from the booster packaging and rule inserts from Nightmares, the FvJ action pack went basically unadvertised, spelling the death of HorrorClix. Shortly thereafter, Topps shut down WizKids, spelling the death of HeroClix and all other WizKids properties.
WizKids would later be bought by NECA, who would revive HeroClix. However, during the WizKids hiatus, many players on It's Wicked Fun took to converting HeroClix for use in their HorrorClix games as a source of "new" figures in the absence of any new sets being made. Converting HeroClix was nothing new, as it had been done since the dawn of HorrorClix, but it was at its peak during this time. Perhaps foremost in this field was Uberman. Many of these converted HeroClix figures, which in most cases kept their point values but rounded up to the nearest five, were exceptionally powerful even with their powers converted into similar HorrorClix powers. This created some degree of imbalance, as HeroClix figures tended to have better stats and powers for the points. However, the converted HeroClix were generally balanced against eachother and many saw this imbalance as a small price to pay for some new HorrorClix figures.
In 2009, Uberman posted what may have been the first attempt at designing a full set, although the project was never completed. Forgotten Tombs was to consist of brand new HorrorClix dials to be put under old Mage Knight sculpts. Fourty figures were listed, of which 15 dials were designed by Uberman.
Later that year, BLG posted Gothix, the first complete fan-made HorrorClix set. The set was designed with the modern set structure introduced in Nightmares, including LEs, a Convention Exclusive and a Buy it By the Brick figure. Shortly thereafter he posted 4 other custom sets; TerrorAsia, HowlingWood, Dark Streets and Tropic of Fear. He is currently working on his 6th custom set, the H.P. Lovecraft-themed Eldritch.