Captain's Pick and Pro Games - Some heroes are not allowed

Hey all, so I'm new to Dota Fire (first post), and I'm relatively new to Dota. I know all the heroes, items, skills, ect and I know a good amount of strategy.

But what I do not know (I love learning about Dota and would like to know) is why some heroes are not allowed to played in Captain's Pick and Pro Games.

I know off the top of my head that Drow and Timbersaw are two of these heroes. But I do not know why.

Can someone please make a list of the Heroes that are banned and why?

Drow -- Im guessing the slow and the skills that make the damage obscene are the reason. Plus the fact that Drow can simply get HUGE damage with farm, and then Silence. (So pretty much every skill is to blame here)

T-Saw -- No idea (Maybe the Pure Damage)?

Again, I really don't know anything about this.

Well, Drow Ranger and Silencer aren't allowed in Captain Mode because they have been recently buffed, and they want to make sure they are balanced before releasing them to Captain Mode.

Also, Timbersaw isn't allowed in Captain Mode yet because he's the newest hero and they have to make sure he's fine.

Hades about summed it up. The only hero missing from Hades list is Slark which is still a scarry hero.

Thanks people!

Captain's Mode is the gamemode used by competitive games.

New heroes are often put on a 'hold' list, to allow the hero to be tested if he is balanced before releasing it to Captain's.

Drow Ranger and Silencer being banned have been stated by hades above.