I understand that the WIPs are still in Beta but in their current state I still think this is necessary for them aswell. Foxy as far as I can tell wins and loses a fair amount and seems pretty balanced to me. But then theres the Panzer. Right now it is losing 99% of the time. Even in the hands of some of the best hale players out there it simply does not have the movement speed and super jump recharge rate to escape a conflict with an ubered heavy + medic which can pretty much wipe the floor of the Panzers high HP due to a very large hitbox. and for this reason I think that the HP mod would most certainly give the Panzer a better fighting chance.

Post your suggestions here guys and tell me if you think the HP mod should return to the WIP Bosses whilst their still in the process of complete balancing.

The HP Mod should return, but that alone wont be enough for the Panzer.
I suggest making him invulnerable against any Uberdamage and adding to that an 5 second uber while raging.
That may seem OP but remember how slow and helpless he is against pretty much every class, I dont even need to be Heavy, an Engineer like me can deal 4k DMG easily just with the pistol by shooting at the panzer from miles away.
You would need a million HP with panzer to win with it in the current state...on full server ofc.

Why can't we finish the boss instead of trying to find a workaround of its current state. I don't support this idea.

Restricting the HP mod from new bosses helps me balance them easier, as I then don't have to factor in their current HP mod when making changes to them, I aim to make new bosses outright just fair, and not have to depend on the HP mod to "catch" major balance issues.

As with Panzer, he's tricky because he's very different, and can either stomp or just get crapped on depending on how the enemy team reacts (i.e., how many people change to medic/ or heavy), I tried giving him charge but it didn't work because his base speed is so slow, so I've given him additional health and crit resistance, hopefully this'll make those ubered heavies easier to survive against.

And while we are talking about bosses, can you maybe buff koishi somehow? or atleast give her more health.

I understand that Blinx about why you dont give them HP mod. But nice to see this post did make a difference and you have changed it up a little because it really did need a buff. Lets see if the crit resistance + more hp will actually make it a more playable boss!