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but the wrangler is already too op, this would just make an invincible sentry as you could have 1/2 engies with dispensers smack metal into this while an engi with a wrangler makes a sentry and as soon as this is attacked a 6th of the metal is used (a wrangled sentry takes a third of the damage) and by the time the attack starts you have 1000 metal in it, two engies ready to repair the level 3 sentry that isnt taking damage until they deal 6000 damage and then the enemies are dead and the engies can start replenishing the metal while the sentry just sits there, waiting to die but its immortal and never will. even if they do 6000 damage, they still have to do like 690 damage (effective t3 sentry health while wrangled)

but since the engies are repairing it they have to do another million consistent damage while not dying

and if the sentry nearly dies the engi can run to a teleporter to a safe place while he rescue ranger grabs the sentry and the other engies just teleport with him

This building looks like a textured version of the scrapped "Repair Node", so how about:

+repairs and restocks broken buildings within its radius (note: repairing/restocking buildings consumes metal)
-50% less healing
-25% less ammo for players (it generates metal at the same rate, but teammates get less ammo per sec from it.)

edit: A couple alternate ideas for attributes:

-cannot refill ammo or metal of human allies (this would replace both downsides, allowing it to heal players at the full rate, but would only use its metal supply to repair and restock buildings)

-building has less HP