I just woke up but here's quesa's guide to remembering invoker
Cold Snap, EMP, Sunstrike = pretty easy honestly, no pneumonic needed
Ghost walk = Glass (q?) is mostly transparent like a ghost but is made by twirling it around (wind)
Tornado = Tornadoes are mostly wind (w) but they need cold air (q) to drop in order to form
Meteor = it's mostly a big ol fireball (e) but you need a little wind to push it around
Alacrity = it makes you all buff like a WWE wrestler
Forge Spirits = they're mostly fire but you need a little ice to hold them together like a comet
Ice Wall = It's mostly ice but eventually heat will make it melt
Deafening blast = it has all the colors in its icon!
Not all of these are perfectly logical but sue me that's how I remembered them