Swain needs a nerf.
There will be many who disagree with this, but it's the truth. You rarely see this because no one plays him despite how strong he is. Not only does hr have a slow and stun, but he also has easy mana regen and health regen. Helped majorly by very low CD's. I know what you're going to go into. "His ult uses a lot of mana." Well his passive makes that not matter and if he gets a chalice, well you're done because then he can freely use his ult. Not even his supposed counter stand much of a chance against him because most of them use a lot of mana and don't have the same regen abilities. First we have Ziggs. Very good against him and has his w for escape, but he uses a lot of mana. Therefore once he runs out of mana all Swain has to do is land his stun right where you can't easily run out and you're basically dead if he has his ult. Second we have Leblanc. We all know how mana hungry she is. Again she has a good escape. It'll only work with mana though and she uses a lot of mana. So lets say this Swain is being super aggressive(which is very possibly due to his passive because he doesn't have to worry about mana). Well you're going to either A) blow all your mana escaping or B) work on being able to walk out of the circle every time. Once you run out of mana and fail to move out once he can drain your health. Third we'll go into Lux. Yes she has her snare, but that doesn't help much because it's just that, a snare. So Swain can still use his ult and stun you if you happen to not be far enough away. She's another champion who uses a lot of mana. Again it's not so difficult to catch someone in his circle. Swain has so much easy sustainability. It's a bout time he got a nerf. Hell most of the times they've messed with him have been buffs.
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+ blue buff on him but he still runs out of mana? Guess what his passive does for him. A tiny bit of mana return in lane, it really isn't as large as you think it is. By design, any champion with a mana return (i.e. Xerath, Karthus, Swain, Kassadin) would have immense mana issues without it.