Eh? I mean, he's not top-tier viable, but as long as you build him properly and run the right summoners, he's pretty good for normals and low ELO. I mean, provided you understand how to play him, because Singed's playstyle is one of the less intuitive out there. What are you doing with him?
As an aside, this is the best way to run Singed, and don't let anyone tell you otherwise:
Ghost+Exhaust/Teleport (depending on the matchup)
Start Flask -> Early Tear (your Q stacks it constantly; past a certain mana level you can leave Q on constantly until it's done, and always make sure to leave Q running in fountain) -> RoA.
After you've got that core done, get Rylai's + Frozen Heart + Mercs + Liandry's. If your team is all doing really well and you mainly need to be tanky, drop the Liandry's for Spirit Visage (thanks to that synergy with your ult plus the extra CDR for ult and fling).
That's hands-down the best Singed build there is. Anything else is either trolling, super-situational, or someone who doesn't know how to build him. You mentioned Ryze, so here's something neat: Singed synergizes even better with mana stacking than Ryze. You get the same boost to your AP from Archangel's, but instead of all that mana giving you pure damage, it makes you super-tanky. That build up there will leave you with ~3.5-4k health on top of decent resistances, being a CC machine, and being virtually uncatchable.
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Playstyle: YOU ARE NOT A DUELIST. YOU ARE A DISTRACTION. YOU ARE THE BEST DISTRACTION.
1. When you're playing Singed, don't try to play him like a normal laner. Your job is not to carefully farm up and trade. I'm not going to try to push the level one proxy strat, because people tend to fuck that up and feed instead of executing. Instead, shove into tower. Always shove into tower, unless it's a matchup with something that can 1v1 you early and easily.
Also remember, Singed has the highest base autoattack damage in the game.
1a. If you can shove into tower, start proxying between towers. This forces the enemy laner to choose between trying to kill you (thus taking heavy damage to their tower and losing farm) or farming under tower (taking less tower damage, but still having it happen). 90% of the time what will happen is that the enemy jungler and possibly midlaner will come top to kill you. Make sure you ward deep in their jungle.
If the enemy mid comes, great. Run away (poison off if you're going to go through their tower range), ghost and exhaust someone if you need to. If you're decently healthy, lead them on a chase through jungle and river with your poison on. Meanwhile, your mid either gets to freefarm or can collapse after you've ticked them down a bit.
If the enemy jungler comes, even better. This gives your jungler free reign to counterjungle the entire bot side of the map, gank mid or bot without worrying about counterganks, or secure dragon. Do the same as if it's the mid. If it's both, even better, you're wasting the time of three people who could be farming or ganking.
1b. If the enemy laner can just jump on you and kill you early (aka Riven et al.), let them shove. Freeze the lane just short of your tower. If they ever try to jump on you or CS, flip them into tower. This is the be-all and end-all of counterplay as Singed, with repeatedly flinging them and running away with poison on as your second best option. Flings into tower are how you'll get most of your early kills and good trades.
2. Mid-game. You've got your tear and RoA and mercs. Just keep farming, farm like a motherfucker, farm all day long. Shove lane into tower, start proxying. If the enemy laner ever leaves, proxy proxy proxy, let all those delicious creeps die to tower. Make sure to last-hit the tower though. This is your big strength: Singed is a perfect farmer, once he can proxy he will get every single cs, which means early items for him. Your goal here is to give the enemy team a choice: send people top or lose your towers.
Obviously if they choose to give up towers or you see 4-5 in mid/bot/drag area, start whaling on the towers. Any time they try to group, take or threaten to take an objective. Once they send people after you, bait them. Taunt them, run back a little bit, pretend to leave, then come back ten seconds later and keep pushing. You need to be pressuring them hard and pissing them off, making them want to catch and kill you. As soon as they go hard, start kiting them on long, winding paths through the jungle. This is why you take Ghost and love your passive: they let you open the gap initially; you should never take flash.
Why? BECAUSE. No, seriously, because your goal as Singed isn't to escape cleanly, it's to drag out the chase and draw people in. You're not supposed to disappear, you're supposed to keep giving them enough hope of catching that they'll keep chasing. This, incidentally, is why Singed falls off against better players: they usually won't chase no matter what you do.
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TL;DR: Your jobs as Singed:
1. Prevent the enemy team from grouping for anything by constantly threatening towers.
2. When you do teamfight (which should be never, if they have the better comp for it--you're good enough to force them to counter your split for the entire game), be tanky enough to run straight into their team, damaging enough to make them focus you, and enough of a CC dispenser to make it hard for them to do much of anything.
3. Land those crucial flips. A good flip (especially if you combo it with your slow for the root) can kill your lane opponent or win a teamfight with a critical pick.
When you start a teamfight, your engage is to pop ghost and/or ult and run at them. Don't try to stop and fight them; fling the ADC or APC towards your team and keep running. Sandwich them between yourself and your team, force them to choose between continuing to run into your (slowing and burning) poison or turning on your teammates. If they keep running, they lose, period. If they turn, you need to react instantly and go back. Use your fling again to grab one of their frontliners and throw them out of the fight. Keep running around through the fight autoattacking whoever is squishy, flipping people out of position. If you have Exhaust, drop it on their biggest threat.
This is why that build and set of summs is so important, it gives you a set of tools which synergizes perfectly with your playstyle. Rylai's makes it much easier to kite people around, escape from ganks, and prevent the enemy team from running away. Liandry's gives you a solid chunk of extra damage to help deal with tanks and more harshly punish people who run into your poison. Seraph's active shield helps you absorb initial burst or bait people into jumping on you. All of that mana makes you super beefy on top of your resistances, and Seraph's converts it into extra damage.
A couple additional tips:
+You root someone if you flip them into your goo.
+Serpentine as you run. The slow from Rylai's will keep them away, and it'll make it virtually impossible for them to avoid your poison. If you're trying to cut off their team for an engage, run diagonally across the lane/jungle path.
+Never use your flip for damage except to coup-de-grace someone.
+Don't level up your slow until level 8 or so. It costs way too much mana to use early on, and will run you dry.
+When using your poison, both to stack Q and to farm, rapid-toggle it. For stacking, turn it on and deactivate it as soon as your Tear goes on the longer stack CD (not the one that refreshes after <1 second). When farming or harassing with it, an instant on-off pop will do the trick for basically no mana.
+Your ult is on a naturally low CD and you build CDR, use it whenever you need it.
+You're like Udyr in a sense. You need to know when to weave in and out of fights, and you need to run ahead of people rather than following right on top of them.
+If the enemy team doesn't have much hard CC, get Swifties, or Tabis against a heavy AD comp.
+In lane, when your own minions are low and the enemy is a melee champion, drop poison on your own minions. Once you have enough mana to run Q constantly, turn the entire wave on both sides into a cloud.
e: HAHAHA, and like a bolt from the blue 5.6 delivers something extra. Singed's E now does lower base damage, but has a 6-8% scaling max health damage on it. That plus the Rylai's+Liandry's build is making him look extra juicy in tank meta. :3
Also 1820RP WAR IS SRS BSNS Teemo skin on PBE, as well as files for a gamemode called "NURF" with a massive debuff.