Prior to playing Arena battles, I stocked up on all of the promotion items needed for Bossk and Dengar. How do I know which promotion items I need for him in advance? I checked my Character Promotion Reference page!
Here's how Bossk arrived at my gaming doorstep:
Bossk has the same vitals as Wookiees:
...and C-3PO, Chewie, Savrips and Trandoshans:
Promotion to Tier 3:
Promotion to Tier 5:
Tier 5 Levels: