are they only situational picks? meaning if enemy laner has mobility/is an assassin, just forget about it?
i'm talking the likes of xerath, vel'koz, etc
i tried vel'koz for the first time yesterday and my biggest issue was how was i supposed to survive ganks, or assassins allins? barrier, E knockup and hope for the best?
i'm new with those kind of champions so any advice would be appreciated
Weak artillery mage are meh at midlane, try playing them botlane instead
Stuff like 
work well mid
The way the current meta is with assassins is basically just dodge or go get a sandwich and wait for the next game.
Buying an early 300g armor item is pretty good investment.
Mostly, don't get poked out by the assassin, play a bit on the safer side, and always remember to ward.
For Vel, his E is pretty good to follow up with a W and Q to the face to show them who is boss.
dark seal.
Well the problem with immobile mages is not them feeding but their team. I feel at least if you are playing an immobile mage that you should be somewhat decent at dodging skillshots.
