So here’s what I did and what I found out:
PS3: level 61 Zero
Summon Terra and haul *ss to the hiding spot behind the rock.
Wait until he spawns. Level 63. Still clueless to my existence, since he never actually saw me.
Split screen, join in with 72 Gunzerker. I’m crossing my fingers, hoping this will be fish in a barrel. Drop down the hole. He stays 63. Sweet! This will be over pretty quickly. HOWEVER, when I start shooting at him, it doesn’t even scratch him. Apparently his health scaled.
He slams me, point blank range, and just knocks my shield down a bit. Whaaaaa?
Apparently, he ranks his health up, but his damage stays the same as level 63.
This is very clever. It allows the 61 player to stay alive (or as much as he would, taking hits from a scaled Terra), but also doesn’t let a 72 come in and wreck things.
Very interesting. So, to answer the question, his “official” number stays the same. Health scales with the highest toon. His damage does not seem to scale.