https://www.youtube.com/watch?v=KTnfN6CRRxQ
All nearby teammates get full crits on their melee (or 2x damage?)
All nearby teammates get a speed boost if their melee is equipped
All nearby teammates get +40% resistance to ranged sources

Of course, this version is OP in medieval mode itself - it'd be like how jarate isn't enabled in medieval. It'd be a direct upgrade to buff banner.

I only came up with this separate stat idea as infinite ammo / increased fire rate is the ubercharge of a medigun I have already. - Though I could always code that too.

The flag model doesn't work, because the appearance of the flag is a bit more hard-coded in TF2 for me to figure out how to replace it.

The horn itself might be held in the wrong position by the soldier, due to plugin limitations.