RTF is a global modification that replaces all towns in the game.

On level 4, you can place Ice Witches (I remember there were also Weather Witches), with the Twilight Witch as the top tier and a Lich as the bottom tier (and make it a 1-cell structure).
And on level 5, you can place Ice Demons (which already exist in the mod and look like Rakshasas) – the only problem is that the upgrades there aren't very logical.