Thanks to an user on a discord channel I remember the name of this old TC: Eternal War. It had 4 races (human, orcs, drows and undeads) and added some new heroes like Doomhammer, Fenriz the Hunter, Ner'Zhul, Rend Blackhand and more and in some missions used cave tileset. The only proof of its existence is this link on internet archives
https://web.archive.org/web/20000528060352/http://www.warclan.com/ratt/Eternal/TC/Ewtc.htmlChances to obtain a downloadable copy are veeeery slim, but let's keep dreaming: afterall Rituals of Rebirth resurfaced after ages
