Transmuter took me ages to get the best out of but I *love* that there are so many ways to build it. Halfling/Gnome ultimate potion spike, Human power-attack-munchkin, Elf mana machine, Orc Binlor knockback monster. Someone came up with a hilarious strategy where you go for a Goblin of GG and absolve the Havendale Bridge Troll.
Transmuter, Crusader and Tinker challenges, especially silver and gold, are right buggers to do.