Electrocute = lot of damage on early game, but still gives you a preaty good late game damage. So the Electrocute is the best - recommended rune. I'm running Taste of Blood, but you could go Cheap Shot IF you were REALLY sure you weren't going to take any damage in the laning phase. The Ultimate Hunter is very valuable to secure the kills. But otherwise you can run Treasure Hunter. That will gives you 570 gold.

For your secondaries runes is really good the Transcendence or Absolute Focus ALWAYS with the Gathering Storm
* Don't take Manaflow Band. Syndra after the rework uses a lot less mana.
** Don't take Scorch. It's really difficult to proc Scorch on cooldown, cause are a lot longer than before. Now looks like short burst trades.

So, the First Strike has BY FAR the most scaling. You have to be patient. Just for that some people think that is a little worse than Electrocute, in solo queue. For this page you' ll be looking to get as much gold you can. Choose the Magical Footwear to save gold for your first item, but you could take Perfect Timing if you're planning on building a zone or something. After choose Future's Market and Cosmic Insight. Αs before choose Transcendence or Absolute Focus with Gathering Storm.

For the Sorcery runes you can actually run Summon Aery, Arcane Comet, or Phase Rush. They all have different use cases. I think that is inferior from the last two pages. So Summon Aery used against for a pretty strong melee champion, cause you can proc it a lot and it's a sure hit as opposed with Arcane Comet.
Now,if you play with Summon Aery than probably want to combine it with Scorch.
But the thing is, you just really can't proc as often as you would like. You're really leaning into that early game. As secondary you ll be taking Magical Footwear and Cosmic Insight
If you have a heavy melee or a tank play with Phase Rush.

At the beginning I didn't understand why I had to maximize W first. The more I played, the more I understood Champion. So I have this to say. If you re beginer, then max E fist. When you're sure you're getting W with great accuracy, then start maxing W.

Your first 40 stacks of Transcendent by level 7 (8 definitely) if you've been doing decent in the lane. This'll be your first power spike, which guarantees an easy all-in if you hit all your abilities

Normally, around the 12-15 minute mark, you will most like hit your next power spike being your evolved W from Transcendent. (I personally do the opposite. I'm getting E Scatter the Weak). Just make sure that you have Luden's Tempest or Liandry's Torment will be your next spike around the 10-13 minutes.

Syndra is not a good split pusher and should never be in a lane by herself farming. It's ok to go to lanes to pick up big waves though. Syndra strengths are, getting picks, objective control, and sieging due to her Scatter the Weak being a powerful zoning tool.

Your evolved E aka Scatter the Weak from Transcendent should be around the 16-18 minute mark. This will now apply a slow after a successful hit, this should help with the Unleashed Power + Scatter the Weak combo in team fights. (As I said earlier, I've already done it, so at this point, I take W Force of Will).

Around the 20-minute mark, you should have your next Transcendent upgrade, which will be your most broken one, Unleashed Power. You now have an execute on this ability when the target hits 15% total hp or less whilst the balls are hitting their face.

Your next power spike will be getting your 3rd item, Rabadon's Deathcap or Void Staff around the level 16 mark. Huge damage boost! If you look at my personal build, you will see that I'm taking Void Staff first, as 2nd item and then Rabadon's Deathcap as 3rd item. I just like it that way.

Your last power spike should be by the 25-minute mark. You gain an extra 15% AP
from 120 stacks of Transcendent.

At this point, your Dark Sphere + Unleashed Power + Scatter the Weak combo in a team fight is a great way to stun multiple enemies and have your teammates finish them off.

Also, at this point, you can easily one-shot a squishy enemy with your basic combo Dark Sphere + Scatter the Weak + Force of Will. You can still try to one-shot a carry with a full combo or, even down them to low health, which will then force them back to base and you'll be able to force objectives as a 5v4. Again, your main tool is Scatter the Weak so use it with caution. If you think someone will get onto one of your carries, use it to disengage. If you think you've got a good initiation comp, use it aggressively.

Thank you for your attention. if I have forgotten something tell me in the comments and I will add it in a future update