Hi @NEmt and welcome to the site and to VFX!
Here’s some things to consider:
Riot uses Photoshop, Maya and their own proprietary engine.
If you want to do stylized stuff, I’d say go with Unity for a game engine to learn because, as odd as it sounds, it’s more limiting than Unreal. Out of the box Unreal has so much complex stuff you can do and I constantly find myself creating new materials to do all kinds of tricks if I need a solution to something. Unity is very limited out of the box for particle and material use, but you can do just about everything Riot does with League’s effects, and it will help you get in the mindset and proper workflow for creating similar stuff.
For Photoshop and Pluralsight tutorials, look for anything hand painted related, even if it’s for environments or props. You will learn some good hand drawn techniques and how to get a stylized look. There are a lot of tuts out there for that.
Piggybacking off what @Partikel replied with:
For where to start with vfx, look at ImbueFX on Youtube. Bill uses UDK and Unreal for the effects tuts but all of the principles of particles, mesh effects and layering apply to Unity. https://www.youtube.com/user/imbuefx
For Unity-specific stuff, check out Sirhaian’s stuff on Youtube. He’s also very active on here as well https://www.youtube.com/channel/UCUqIetx0scoe79qZTovn9BA
Shannon works at Riot and posted here demo reel as well as some breakdowns of the effects she’s done, and is usually good about answering questions on the thread there.
Jason is another VFX master over at Riot, you can find his hand drawn flash fx tutorials on his Youtube channel, which applies both animation fundamentals and to the hand drawn flipbooks they use on League:
As for one last link, Sirhaian shared all his league fan stuff for people to download and learn from, and that thread is here:
Any other questions, feel free to ask away and we’ll help as best we can! Best of luck getting started, and feel free to post any progress you make 