Once you hit level 6 in Darksiders, you unlock Reaper Form (You know, that thing you've been transforming into in the boss kill cinematics?), which is powered by Reaper Energy.

Great! So how do we earn Reaper Energy to recharge the ability? The in-game tooltip mentions that you need to use Reaper Attacks to gain Reaper Energy... and then totally fails to explain what a Reaper attack actually is.

So what is Reaper Energy, and how can you acquire it? I've seen a few Wrath skills mention it, and a few weapons have +reaper energy on execute, but I don't have access to those things yet, so I need a way to accrue Reaper Energy in the mean time.