Active spells in the alchemist. Look at the thread titled Spell Guide Info, under questions and feedback section for more info.
It allows you to change your name color, hide you allies, get increased chance to make your enemy lose more gold, and adds to your stats. To use it, you need 25 lands, and a 4b castle upgrade. This unlocks the alchemist where you can spend collected mithril.
viewtopic.php?f=8&t=94249&p=2742033&hilit=complete+mithril+guide#p2742033 Here's the complete guide on Mithril. You're welcome.