So, I know that Magic Circle against Evil acts as an emanation, and everyone within a 10 foot radius of the target gets the effects of Protection against Evil. Additionally, non-good creatures cannot enter that 10 foot radius circle (at least not without making a check).
What my party and I are unclear on is whether or not it is possible to make attacks while within the Magic Circle. The description for Protection against Evil says "The protection against contact by summoned creatures ends if the warded creature makes an attack against or tries to force the barrier against the blocked creature." If I'm interpreting correctly, this seems to mean that characters cannot attack while under PaE, or else they will lose the benefits thereof. However, with MCaE, there is the additional effect of a 10 foot radius circle in addition to the personal PaE barriers, right? (Or am I mistaken about that, even?)
So, how would attacking work in this case? If Archibald the Archer fires an arrow while inside the MCaE, does he lose his personal PaE barrier, but creatures still cannot reach him because of the outer circle of MCaE? In that case, of course, enemies firing into the MCaE could target him, and he would no longer have the deflection bonuses of PaE. OR is it the case that you can't use ranged attacks while within the MCaE without breaking it? What about spells? What about melee attacks used at the periphery of the circle?
If someone could explain just how combat options affect the integrity of the circle and its barriers, I would greatly appreciate it, as the descriptions are very ambiguous to me.
Best Answer
Looking through the rules, it seems that by a lawyerly reading of MCaE, the "protection" version of the spell (as opposed to the "prison" version; more on this in a moment) essentially has two effects: a mass PoE, and a circle that certain summoned creatures cannot enter.
The mass-PoE effect seems to be essentially unaltered from the original spell, except that it only applies to creatures inside the circle. If you walk outside, you lose the effect; if you walk back inside, you get it again. This makes the personal protection against bodily contact a moot point. One could argue that it technically still exists, but it only applies while you are in the circle, where there is already another barrier in place. Because the circle is not linked to you specifically, it does not collapse if you reach across the circle to attack.
Speaking of reaching across the circle, both PoE and MCaE are very explicit that they only apply to the creatures themselves. Ranged attacks are fair game. Even an imprisoned creature, in the "prison" version of the spell, is explicitly stated to be able to make ranged attacks across the circle, as long as they don't target the circle itself. So yes, creatures inside an MCaE can make ranged attacks across it, but so can creatures outside an MCaE.