Anyone play tf2?

I'd completely overhaul spy. I'd keep his primaries mostly intact, possibly considering adding one more that deals more damage to buildings (+20%) with a penalty (-20/-10%) to players. 

I think it would be interesting to see how people would/would not utilize it.

An update to how knives work (what constitutes as a backstab) would be cool, but I could easily see that causing an uproar in the community. I'm not saying I hate how it currently works, I just think a change like that would shake things up and I'd like to see how it would change spy game sense. (Maybe even knife headshots)

For knives, I would add two: One with bleed damage to yourself and (possibly) the other player and slower swing speed but with the benefit of a small health and cloak boost (+15%). That way, every stab that isn't a successful backstab would be penalized. The second would be dealing more damage based on your cloak. The closer you are to 0% cloak, the harder you hit. I think it would incentivize riskier plays while also encouraging cloaking as much as possible.

I would make the disguise kit a little more stylistic, like character-themed cigarettes or a nice reskin. I don't really have much to change about it. 

I wouldn't change any invis watches but would consider adding another sapper, somewhere between the red-tape recorder and the stock.