For the record: Dispel Magic
A typical Communal Spell: Resist Energy, Communal
Very simple. Dispel Magic mostly says that you are targeting a spellcaster, creature, or object, but under the Targeted Dispel it also adds that a 'spell' can be a target.
So, suppose that I am a BBEG, and I am facing a party of players who, knowing I like acid spells, has put up Communal Resist Energy (Acid). Can I use a single Dispel Magic to try and unravel the acid resistance for the entire party by targeting their Communal Resist Energy, or no?
No.
You can also use a targeted dispel to specifically end one spell affecting the target or one spell affecting an area (such as a wall of fire). You must name the specific spell effect to be targeted in this way. If your caster level check is equal to or higher than the DC of that spell, it ends. No other spells or effects on the target are dispelled if your check is not high enough to end the targeted effect.
Communal Resist Energy is not an area spell, so you have to do your targeted dispel on a particular target creature.
yeh - it'd have to be something like fog cloud that takes up an area and has a lasting effect for that bit to be used - greater dispel magic could be used for what you want though as you can if desired I think remove a chosen spell for each target