This Challenge requires you to kill Threshers, which are the squid-like creatures. There aren't many spots where they frequent, making this Challenge a bit of a chore. Some spots where you can find a decent amount of Threshers include Caustic Caverns and Sawtooth Cauldron.
- Rank 1: Kill 10 Threshers
- Rank 2: Kill 25 Threshers
- Rank 3: Kill 75 Threshers
- Rank 4: Kill 150 Threshers
- Rank 5: Kill 300 Threshers