Purchased from Spoils Collector (The Pillars) for 99 Brass Sky Pirate Spoils.
Gives you stuff for completing certain achievements. Talk to him occasionally.
I had to do two leves to get this one to show up. I don't think it matters which ones.
If this doesn't show up right away, just do a random leve and it'll be there next time.
Stupid easy, especially with chocobo. Just remember the timer doesn't stop after you kill the minimum. Keep going until the time runs out.
Spawned at about 11:35EST.
Popped at about 11:30 EST, after Bush Blade ended without success.
Spawned around 8:15EST.