Sorry, I meant Reaper's XP not your character's XP. From what I understand, your character gets experience based strictly on the number of units you wipe out regardless of how you do it. But the spirits of rage gain xp based on the skills they use AND who they use it on and several other factors. So it's very easy to level Zerock with Underground Blades, especially if you're hitting level 5 units. Reaper is also easy to level if you use Soul Drain on say Black Dragons or Black Hole on level 5 units.
My Reaper didn't hit level 30 because I used Time Back 95% of the time, and Rage Drain the other 5%.
