Skywrath's Ultimate

I like schyte or Bloodstone. Hmmm i think the best friend for Skywrath Mage is Legion Commander Skywrath Mage got kill and Legion Commander got damage (using Duel)

Well, 6 second silence is SOMETHING against invis heroes, your point is: don't ever pick squishy supports against Riki, which is kinda ********. I think he is great against invis heroes, of course, with lot of sentries and ideally a gem.

Because of the silence I think Skywrath Mage is one of the best heroes to counter Riki. The best counter in teamfights is probably a core Silencer since you can prevent Riki from being invis AND from blinking plus your dps can bring Riki down really fast. Since it'd be a core Silencer a BKB would also be available, stopping Riki from silencing you.

Rod of Atos is your first core item on Skywrath Mage. I'm not even joking. Bonus health to keep you alive, a lot of INT to increase your mana pool and up the damage of Arcane Bolt. The main thing, though, is that it gives you a 60% slow from ludicrous range. Couple that with Concussive Shot which is a 45% slow from ludicrous range, and boom. You get a full length Mystic Flare on someone, or at least a very good shot at it.

When it get's later, and if you have a No.5 who is going to be a complete ward jockey, and if you have a gem carrier then sure.
Unless you have a Force Staff Riki can kill you in his cloud. Early game at least. I may have been a touch over zealous when i said all game long, but if you want to be (potentially) very ineffective in early game. For someone who is amazing at early roaming that is pretty terrible.
Force Staff > Rod of Atos > Black King Bar/ Ghost Scepter/ Aghanim's Scepter is generally what i go.

He can be picked against them, but there are much better.