Its a trophy. You place it on your plot or house (if you have one) and then bring up your tribute screen and use one of the Tier and it will add that stat when you have tribute running. It doesn't "evolve" - it already is what is is.
Here is info on tribute. There are quite a few trophys given out as rewards
Trophy is an achivement reward for House of Thule task called Savior of Erudin Burning (40 Points) Navigate to Achievement Window > General and scoll Seven from bottom
Tier 1: Heroic intelligence 6 and mana 50 Tier 2: Heroic intelligence 8 and mana 75 Tier 3: Heroic intelligence 10 and mana 100 Tier 4: Heroic intelligence 12 and mana 125 Tier 5: Heroic intelligence 14 and mana 150