[quote=@vancexentan]
The idea is the servants go in first, clear out the more physical obstacles, Monica, and other illusionists/skilled masters dispels them, we move forward. The Greys are directly in the middle of a circular forest. There is no going around them, and they're purposely holding themselves shut up in their own territory. They're forcing us to attack them in their territory in order for this war to actually continue. The enemy servants uses the traps, and defensive terrain to pick their fights. Some of the aggressive ones may make bolder moves. 

The true danger lies in the servants being backed with fake images, and hampered terrain. They are also effected by it but know better because they're aware of what is where.
[/quote]

I see.

But why is it that Caster can't be the one handling any harmful spells instead of putting humans who can be killed by a breeze (from the point of view of a Servant) in harm's way?

Also, while I see these issues, I still ask you to understand that Atalanta won't be significantly impaired by illusions and bad terrain. Or rather, knowing her feats in canon (again singling out Jack inside the Mist, especially when Murder of the Misty Night and Presence Concealment are also part of the equation, is supposed to be nearly impossible to do). And as far as bad terrain goes, that's the sole reason why Crossing Arcadia even exists, to cross through incredibly bad terrain (and even jump over enemies in battle) while suffering little to no impediment.

I'm not trying to trivialize your obstacles, but in this case, Atalanta's skills and abilities are more or less a serious counter to everything you mentioned. And that's not even taking her Archery into the equation.

Again, I don't doubt that a Caster can make it hard for her to navigate around. Hiding in a hole behind tons of bounded fields is more or less what Casters are *supposed* to do best. But illusions (regardless of grade), traps (since she does know how to lay traps to hunt Phantasmal Beasts of Age of the Gods caliber, even if she doesn't have the tools to lay them down while being summoned as a Servant she still has the experience and senses to notice them way ahead of time), and uneven terrain, are things Atalanta is perfectly equipped to deal with.