Spy's secondary slot is very unique in the way that it's a gadget that only has one use, and only against one class on enemy team. As a result it's the same in balance as Darwin's Danger Shield or Razorback in live TF2, which isn't a good and fair design in general. Here is the topic for discussion of how to overhaul it and fix it being so onesided, and my personal suggestions of such overhaul:
[SAPPER]:
- Make sapper affect other game mechanics outside of engineer's buildings. For example, add an alternative attack which would throw sapper on the ground and create a radius in which certain things would be disrupted. Possible disruption effects:
- Stickybombs and mines explode with long delay arter pressing detonation key (1.5-2 seconds);
- Dynamite Pack takes 1.5-2 more times longer to explode;
- Cyclops EMPs fizzle out instead of exploding while in the radius;
- Buildings operate slower (lower sentry RoF and turn speed, longer teleporter cooldown, lower dispenser heal and resupply rate, lower jump pad jump height);
- Shock Therapy restores half or third of the normal health on hit;
- Spy cloak drains 33-50% faster when inside the effect radius;
- Enemy sappers deal 33% less damage to buildings;
- Sniper rifle charges up 2 times longer.
- Cooldown time for throwing: 15-20 seconds.
- Sapper is killed by 2 wrench hits in thrown mode.
[TRANQUALIZER]:
- Put tranqualizer gun outside of the primary slot, since it is overshadowed by revolver in almost any situations. Put it either in sapper slot as an unlock, or into it's own gadget slot. Changes for tranq gun:
- Shooting tranq doesn't drop disguise;
- Tranq effect no longer applies melee crits to enemies;
- Reduce tranq ammo reserve to 4 to prevent mindless spamming;
- Tranq shots disable building for 0.75-1 second;
- Reload speed reduced by 20-25%.
This way sapper would have some uses outside of engineer engagement, and tranq would be less underused due to revolver being better.

