Ballista-1 is an Elite Boss who works for Longbow.
The Ballista are Longbow's heaviest hitters. These tankers are tough enough to withstand direct hits from rocket launchers, and can dish out enough damage to take out the toughest brute Arachnos can throw at them.
During the Help the Sky Raiders fight off Longbow he says the following:
Before combat: Unit 1 here. I've been unable to confirm contact with Villain.
Combat start: Unit 1 calling in. I can now confirm Villain is in the kill-box. Engaging.
At 75% Life: Huh.
So when do you start fighting?
At 50% Life: I'm going to have to upgrade your threat rating from "Harmless" to "Mostly Harmless".
At 25% Life: Is that...
Is that the best you got?
Defeated: Fair's fair.
You got me.
After defeating a player: Unit 1 calling in. I have neutralized a threat.
Well, "threat" may be a bit much