Kassadin skin ideas
My brother is a 
main and is sad about the lack of skins so I tried to think about skins for him and these are the skins that I thought of :
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Officer Kassadin - Null Sphere effect would be a doughnut or a taser shot, Force Pulse effect would be pepper spray, his blade would be a cop's club / baton ,trail would be...wanted posters flying around? (similar to Lissandra's ice trail), Riftwalk effect would be...some police car that appears and vanishes when he teleports...?
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Frozen / Frost Kassadin - Null Sphere effect would be an iceball covered in spikes, Force Pulse effect would be some freezing wind, his blade would be made out of ice (obviously) ,trail effect would be some cold mist (like when you open the fridge, lol), Riftwalk effect would be more cold mist when he teleports.
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Safari / Jungle Kassadin - Null Sphere effect would be a compass, Force Pulse effect would be vines, his blade would be a machete or a survival knife, trail would be....again some vines (like Lissandra but vines instead of ice), Riftwalk effect would be some vines appearing and vanishing while he teleports.
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Dark Lazer Kassadin (Darth Vader reference) - Null Sphere effect would be...some blue lightning orb? maybe just the normal sphere..., Force Pulse effect would be blue lightning, his blade would be a red lightsaber, trail would be...more blue lightning? or just his normal trail in red..., Riftwalk effect would be a hypergate that appears and vanishes when he teleports.
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Surgeon / Doctor Kassadin - Null Sphere effect would be a bandage roll, a pill or maybe a bottle of some medicine, Force Pulse effect would be...some kind of gas?, his blade would be a scalpel, trail would be similar to Officer Kassadin's just leaflets instead of wanted posters (the papers that come with a medicine containing information on it), Riftwalk effect would be...a lab door that appears and vanishes when he teleports.
Nether Blade would just be some visible aura on the blade.
His clothes for each skin...well they would need to fit the skin - dark clothes (cape !) for Dark Lazer, dark-blue clothes for Officer, lab coat for Doctor, yellowish khaki clothes for Safari, cyan-white clothes for Frozen..maybe clothes made out of ice...sort of.
Use your imagination, I'm sure you will be able to see "it".....I can see "it" however I don't have the drawing skills to make sketches =/