Hello! I'm Bartoos and I've been playing Syndra regularly since season 7. Over the years I've accumulated 150k+ points on her (on several accounts) and still enjoy playing her as if it was my first game. I decided to make this guide to help people get better on Syndra.
This is my first guide ever on this website so I'd love to hear your opinions. Let me know if there is something you'd like to see in this guide!

These are the items you want to buy at the start of the game. Buy Corrupting pot against enemies that outrange you, like Vel'Koz, Ziggs and Xerath. Take Dorans Ring against everyone else.
This is the most basic build you want to build almost every game. You can swap the order of these items around depending on your current situation, like you can rush Zhonyas 2nd or finish Morello 2nd etc.

These are the situational items.

You want to build Mejais if you get a few kills early on. You can easily snowball and get so much value off of this item no one will be able to stop you.
You want to build Rod of Ages and Seraphs Embrace if you're facing an assassin and you're really not confident in yourself. This will lower your overall damage output but it will grant you a lot of extra survavibility.
You want to build Banshees if the enemy has 1 specific spell that will be the end of you when you get hit, like a Lux Q or Ahri E.
You want to build Liandrys when the enemy team has a threatening amount of health. I t will also increase your burst by a lot because of the 10% increased damage passive.
You want to build Rylais if you're not doing too well and you need the extra survavibility while providing utility for your team. This item works even better with Liandrys.

These are the items you want to buy when you're going Phase Rush. This aside from giving you movement speed from runes will give you extra utility and slows. You can also switch the item order or buy situational items.

Honestly I'm not sure why do people even bother making sections about how abilities function when this can be so easily researched individually. You can learn how Syndras abilities function here -> https://eune.leagueoflegends.com/champions/syndra/
I'll give you the exact math behind Syndras abilities here though.

This is the most optimal rune set for Syndra. If you don't know what to choose just go with this.
If you're facing a melee opponent that is easy to poke like Kassadin, take this rune page.

And if you're confident in your ability to use your kit in the best way possible and output the most damage you can you should go with this build that gives you enough mobility to escape most sticky situations. With this rune set you also want to buy Hextech GLP instead of Ludens Echo.

Depending on the matchup you can play your laning phase a few ways.
First of all, lets start with the easiest match ups. The champions listed as threat level 1 you can absolutely stomp. With these champs you can be pretty reckless and hard push the lane and poke/burst em' out of lane. Be careful not to go overboard with it though, the enemy team still exists and you can always get ganked. If the enemy jungler is being problematic you can just hard push and roam.
Champions listed as threat level 2 are pretty much like level 1, although there are some scenarios where they're able to outplay you and kill you. Like for Akali it's her having Gunblade, ignite and ult. You can always push her away on her engage though.
Against champions level 3 is where it gets tougher. You need to stay focused and watch out for specific abilities that are really dangerous for you, like an Ahri Charm or a Morgana bind. If you manage to dodge their main abilities you'll be able to stomp the lane. Some champions pose a threat due to their ability to set up ganks, like LeBlanc and Lissandra, or their amazing roaming potential like Talon and Qiyana. Against the easy gankers you want to stay a bit back and don't go too far into the lane. That will discourage the jungler to come. Against roamers you want to shove the lane under their turret constantly and roam or help your jungler with objectives.
Against champions listed as threat level 4 you want to play defensively (except against Kassadin). Stay back and just clear minions and look for opening to poke the enemies from a safe distance. In the case of Diana, Irelia, Pantheon you can just stay back and E them if they dash to you. In the case of Lux you just want to farm and wait for her to overextend. Kassadin though, you need to be as agressive as possible. You need to constantly poke and harass him out of lane so he doesn't get any experience and gold. This will set him really far back in gold and he won't be able to kill anyone on a roam.
Against champions level 5 you basically don't stand a chance. Just sit back and farm, poke if they mess up but never get close enough for an all-in. Against the long range mages you might wanna go corrupting pot and cookies, then buy a dark seal to outsustain their long range poke. Stay completely focused to dodge any abilities coming your way.

The mid phase for Syndra is the most important stage of the game. Depending on how you played your early game the mid phase can go one of two ways:
-you got a few kills and/or a lot of farm and you can snowball really hard. You want to start roaming all over the map, instakill people and get objectives. You are really good at doing both of these things because of your insane burst and area-of-effect crowd control. Play around your team so the enemy team doesn't catch you in a 3v1 where you're most likely to die. Even if you're snowballing, you shouldn't always go straight up damage. If they have an AD threat like Talon or Zed you should always buy Zhonya's second. IF the enemy team is starting to buy magic resist, you can go for Void Staff.
-you got killed a few times and don't really have that much farm. At this point the best thing you can do is sit mid and farm. If the enemy team leaves for a roam you can shove the wave ASAP and if you don't know where they're going, push the turret. If you do know however, follow them through a safer route so you don't get caught. You still have enough damage to make picks with your stuns and kill enemies with your team. You want to play safe and stay behind your team though so you don't feed any more.

This is why everyone hates Syndra. Her terrific late game. At this point you can stack a few balls and ult the enemy carry and instakill them.
Jokes aside, you focus on clearing lanes and making pressure and force the enemy to clear lanes. When an enemy or 2 are gone to clear lanes it's time for you to start a fight. During a teamfight you don't want to overextend because it will always end up in your death. Only get closer if your team or you manage to land a CC ability on multiple people. Beat up the front line with your 0 cd spells. Keep your R for squishy targets that will actually take damage from it. Also keep in mind to never go alone through risky routes. There is always a chance someone will be camping that bush you're about to facecheck.

These are the optimal warding locations if you are blue side. Consider warding a bit deeper, like around the red buff/raptors if you are snowballing. Also consider warding raptor camp and behind the wall between river and wall next to turret.These are the optimal warding locations if you are red side. Consider warding a bit deeper, like in the raptor or red buff bush or in the bush behind olves if you are ahead. Also consider warding behind the mid/jungle walls if they have a Zac.

There will be videos coming very soon, stay tuned!

Base Syndra

Outstanding. Beautiful. Gorgeous. 10/10

Justicar Syndra

This skin has a nice model and some pretty effects, although it is pretty pay2win because the effects aren't very clear. 9/10

Atlantean Syndra

The effects are pretty although the model looks kinda dirty. Also pay2win due to decreased visibility in the river. 7/10

Queen of Diamonds Syndra

No. Just... No. The effects are like base Syndra but the model and splash... 0/10.

Snow Day Syndra

This is definietly one of her prettier skins. The splash art is cute, the model is cute and both the visual and sound effects are satisfying. Also pay2win on ARAM. 10/10

SKT T1 Syndra

I rarely see this skin in game but since it is one of those Worlds skins that means it sucks due to the rushed design and ugly logos everywhere. 3/10

Star Guardian Syndra

The effects are close to the original skin but the model is pretty cute. Also her ult sounds like water balloons and that's fun. Also her orbs make an UwU face sometimes. 7/10

Pool Party Syndra

Like any other Pool Party skin, it's dissapointing because the designs are really lazy, but this skin isn't all that bad. After the update to her effects it's not just an Atlantean Syndra chroma, so that's an improvement. 6/10

I hope this guide helped you better understand and enabled you to get better on Syndra. I'd love to hear opinions on this as this is my first guide so please leave a comment! Let me know if this guide is lacking anything and I'll make sure to add another section!