I have been playing spy for 200hours Total playtime even before steam release and I still think Stock Revolver still out shines Post Tranq for its damage, hitscan and range. Revolver can speed kill buildings while sapped, reliably finish off the wounded, safe range to chip damage, burst enemy players close up, destroy Demoman's stickies and etc.
The Tranquilizer doesn't have much benefits to what the revolver gives. Its stealth quality is lacking but just draws more alert to spy just so he could face stab a player. It alerts people before the stab. The more experienced players you face the Traq becomes less beneficial. Its hard to hit players with projectile with slow reload, tranq darts can be evaded can leave you defenseless, tranqed medic can just knockback serf away from you, Medic can cut duration effect on tranqed allies, tranqed enemy just remove the effect thx to close by health packs, overhealed light classes cannot get oneshot stab, more of a hassle when trying to deal behind enemy lines. Its only extension is taking out isolated player and more useful at fighting spys thx for its predictable patterns, when tranq cant retaliate when cloaking and even still have the effect shown while invisible. Going behind enemy back lines to kill high value players and destroying buildings makes you feel like its to forgo the tranq from its unnecessary participation.
Buffed Tranquilizer
Make tranquilized enemies do not scream in pain or on death. A way to catch players off guard. Maybe it could even remove the kill feed notification if you hit someone with a max-duration dart? It would be interesting if we allow it to be fired while stay disguised as well. The visual colorblind effect already makes it obvious to the player that there is a spy. And this would also play nicely with the crit on melee hit. Making it easier to kill targets when you hit them, at the cost of making them super paranoid. Overall I think it wouldn't hurt to try this change.
