Many of you guys sharing their ideas and concepts of their custom weapon concepts, so I decided to share too:

+ Spy can waltk through enemy players and buildings while watch is active.
+ Attack and Alt. attack perform same actions as current weapon of disguise character while watch active.
(For example: While disguised as Heavy that is holding minigun, holding alt. attack will make his minigun spin and attack makes him shoot fake bullets)
+ Spy can shoot fake projectiles/bullets/flame particles of disguised character. They look exactly the same as real, but deal no damage and healing, have no knockback and don't interract with anything.
+ No bloodstains and impact sounds while watch is active
+ 100% resistance to knockback force from explosions and bullets while active
+ Afterburn immunity while active
+ Can use sappers while active
+ No noticeble signs for enemies when watch activated or deactivated

- Doesn't make Spy invisible
- Cannot be activated while not disguised. Disguise required.
- Can be activated only when charge is 100%
- Watch cannot be deactivated once activated, alt. attack is not for watch deactivation
- 85% less charge from pickups and dispensers
- Spy takes 20% more damage while watch is active

As we know, watch is used for invisibility to get behind enemies and disguise is used to move among enemies. But disguise sucks in tricking enemies to make them think you are truly one of them. This watch solves this problem. In cost of ability to be invisible, it makes Spy's disguise more versatile. You can pass through enemies with confidence, pretend doing spycheck or shooting other team. That makes disguise more accurate, it gives more space for maneuver and enemies would never know are you a Spy or not until they kill you. It should completely change feeling of playing spy, bring new tactics and will make the enemies more anxious.