Coliseum normal battle

That subroutine will cure all negative statuses, but it excludes MagiTek and Interceptor status because those statuses are intentionally set and not considered negative. The game still uses this subroutine while Magitek & Interceptor status is applied, so you wouldn't want to remove those ones, right?

I'm not sure what the second part of your sentence is describing. You want to cure negative statuses such as poison, dark etc. before entering a coliseum match? If so, then you would do some event-coding to add that subroutine in question before the match takes place. This is event editing and it's a time-consuming nightmare to try and teach someone simply over forum posts lol - it's not going to be a simple byte change, you'll have to know what you're doing basically. You could take a look at some tutorials on the wiki if that might help you learn:
https://www.ff6hacking.com/wiki/doku.php...ial:events

And then ask questions as you go. Basically it involves using a hex editor and referencing the event dump document which is a disassembly of the entire event code.

I want to cure all negative status, but every coliseum match does not remove any negative status. I let Gau have poison & Dark status before enter a coliseum match, but no cure.