The main antagonist of this part are the Pillar Men. Though they are extremely powerful, sunlight (and thus Hammon) is lethal to them. Therefore, Kars, their leader, seeks the Red Stone of Aja to become immune to it. After using it with the Stone Mask, he ultimately obtain such power, but was killed when Joseph threw him into a volcano.
Correction
Um actually … Kars didn’t die in the volcano. The volcano eruption propelled him into outer space which froze him and incapacitated him.
Got this one. Seasons 1 and 2 are very memorable.