Despite popular belief, Madstone is worth your gold to purchase on Fiora, especially on TT where Vilemaw is such a crucial chokepoint to victory.
As you know, Fiora is quite squishy and doesn't stand a chance in fights. That's where the Frozen Heart and Mallet come into play, even giving her some much needed CC to boot.
The Grez's Lantern also adds more to this build. As you can imagine, having both of these frozen items could really chill down a champion, thus comes the Lantern's warm flames to keep her blood boiling for the fights to come!