Wizard – “The Triumvirate” [Campaign 6, Mission 3]

Zeratul, to level up Godrick to level 24 in the first campaign, you need to explore the entire map, including the dungeon. In version 1.5, he could be leveled up to any level if it weren't for the level cap. I don't know how it is in 1.6, but in 1.5, enemies never flee the battlefield. They appear in groups of 2-3 every week. You can level up indefinitely.