I happened to be browsing FEditor’s text, as I am wont to do, when I stumbled upon this seemingly-unused text:
Welcome to the arena.[.][A]
Oh! It’s you again.[.][A][0x02]
I’ve lost a lot of gold[.]
thanks to you…[A][0x02]
If you want to continue,[A]
we’re going to have to
do things differently.[A][0x02]
I’m going to prepare some[.]
more challenging foes.[A][X]
After a bit of debugging, it seems that if bits 0x8 and either 0x2 or 0x4 (or both) of byte 0xE of ram character data are set, that unit unlocks Super Arena mode, along with some interesting text glitches:
Without those bits set (paid 820 gold)
With those bits set (paid 890).