Interesting

ooh i like that idea!

Eh, little OP. Imagine a sapper that has more HP and can run away from the engi. Also you should be more specific. Like if you were cloaked, then you could still do this? Imagine an invisible sapper that could run away that aslo has more hp. Oh! And this sapper could shoot at you and kill you. (Mind the sentry flip up time. Thats 2 shots easy).

if this weapon is added: ennemi engi can find you more easyest with damage and absence of sapper, check around dispenser

did you just specify the range of the effect?

I think this video should tell you why this is a horribly OP idea:
https://www.youtube.com/watch?v=dSVRlAFTmUQ

A idea that's very specific, King. While of course there are alot of ways to consider this. on one hand, you can shoot and do more things while still being able to cause a ton of chaos for the engie. On the other hand, if you die then the sapper won't stay on, and your sap attempt is ruined.
An idea I had was that there is a charge, built up over time (Can't recharge via resuply locker, would be too constant) When fully charged, you can activate a AOE EMP which disables sentries (but doesn't do damage), reveals cloaked spies, and creates a small auora around disguised spies. The downside is that until the EMP has faded, (3 seconds) then you can't use cloak, sappers, or disguise kit. This item is to make the spy more of a team player, will still getting the enjoyment of causing chaos amung teams. I would think it would be a great item to use if your team is getting camped, or if you are being held in place. Also if good if you just want to go behind enemy lines like spies normally do, and just disable everything.
Oh and another thing, you still have the stats and abilities of a normal dead ringer, but slightly altered, probably a louder uncloak. I also think it would be funny if it had the Nokia Ringtone uncloak sound.
Jesus christ that was a long comment.

That's not a very good idea, that would'nt be balanced and hard to counter

the idea is interesting, but the way you proposed it is too OP

slowly damaging the engineer buildings while cloaked is a fun concept, you'll force the enemy to look for you and make a good distraction

disabling the building is too powerful, but damage over time seems good. To make it effective the cloak should last a bit longer than stock, but to make it balanced maybe 10 less health to make the hide and seek easier for the enemy?

on backstab instantly cloak and remove status effects
adds silent kiler
no other downside (the cloak on baskstab wouldn't really allow chainstabs)