I came up with an idea for a skill. My first idea was this.
Applies 400/600/800 radius truesight around all enemy heroes on the map for 3/4/5 seconds. Cooldown 120/110/100 seconds. Manacost dependant on which hero you give this too.
My second idea was this.
Targeted place on the map gets revealed with a 500/600/700/800 radius, whereas 100/150/250/300 is truesight for 4/6/8/10 seconds. Cooldown 40/35/30/25. Same as above with manacost. It works pretty much like the scouting skill terran has in starcraft.
I think this is a pretty unique skill which can prove very useful vs invis heroes, checking runes, scouting the map etc. It will surely add some more diversity.
Just thought I'd share my ideas.