These are by far my favorite mission type
they play very differently than the rest of the game. Range and piercing is much more important than damage. Spell's range is based on a "time to live" mechanic, this means that "enhanced projectile speed" also increases the range of your spells, since they travel farther in the same time. Energy Slice has great range and pierces, so it is my go to spell for JtP.
Miniaturize is another great spell for these, since the increased damage is meaningless, yet the greatly reduced hotbox size is invaluable.
Vision is your most important defense. As was already mentioned, a "reduced detection range" of greater than 25% acts as enemy radar. That, coupled with having the screen follow the mouse should let you much farther than usual.
As for the large cliffs, there is usually a point where they cut back in, and leave some background space you can stick a platform on. Remember that platforms stack, so you can create a "Lemmings Bridge" with them is you overlap their corners. This will stick far out past the edge giving you a purchase within vision.
If there isn't the room for a platform bridge to grab purchase, just start chucking crates
Eventually you'll see them poking out from the bottom of the screen and you can create your bridge from those. Platforms and crates stack nicely, and don't fall over no matter how slanted you make your stack.
Hope that helps, and wasn't too redundant with the others.