I tried out the Arena just now, and was getting frustrated because even though I had two of a given Model/Companion, they weren't combining, making fights against later bots impossible. Then, with the help of a forum topic, it was explained that the cutoff is three or more of a given Model/Companion, not two.

The tutorial currently says “Multiples of the same model will combine automatically to achieve higher levels, with 3 stars being the max level.” This was unclear to me, because I understand “multiples” to mean “two or more.” I would recommend that for clarity this sentence be changed to something like “Three copies of the same model with the same level will combine automatically to achieve higher levels, with 3 stars being the max level.”

FULL support oh man. literally had the exact same experience and had to scour the forums for the same thing LOL i just figured i was doing something wrong and got SUPER frustrated at being seemingly unable to level my models u_u

Agreed. This also confused me, and I only figured it out by reading a guide on the forum.

-The tutorial uses characters at the start and models at the end when it should be just using characters for clarity's sake. Especially when character and model have entirely different meanings.

-The tutorial should also clearly state that 3 characters will combine thing.

I had absolutely no idea how the characters combined in the arena when I played it for the first two times, it was so confusing and I read the tutorial. I even thought the characters will only combine when you buy a new team member? I mean yeah but not like that lol. The star symbol that appeared on some chars but not others was also adding confusion to the mix. It's so necessarily weird because when you do understand the mechanics it's like…well that's actually easy.