Warhammer 40,000: Dawn of War II - Retribution
77 Achievements
GOG
Summer Slaying
Kill 5 Banshees on The Bloodied Colosseum.
1.5%
How to unlock the Summer Slaying achievement in Warhammer 40,000: Dawn of War II - Retribution - Definitive Guide
Banshees are a common Eldar (elves) enemy type. They're the females with coneheads. They spawn in groups of four. So you'll need to kill two spawnings of them.