This is the formula for every major fairy-tail arc as far as I can see. Reading this weeks chapter, watch how this plays out.
Step 1: The guild is attacked.
Step 2: The person attacking the guild will win versus at least half the guild members with some overpowered ability. This week it is "spacial magic control", in the past it's ranged from gravity control to gorgon-eyes.
Step 3: The guild will take revenge. This may or may not require capturing the damsels in distress.
+ If Erza is a damsel, she will break free
+ If Lucy is a damsel, she'll help out at the end of a battle.
Step 4: Mid climax of a battle, some "dark magic" will be used to up the ante. It never succeeds no matter what it is.(a giant robot, apocalypse bomb, you name it).
Step 5: Natsu will generally win some fight by eating fire or just being "extra pissed", this fight is generally the last boss.
Step 6: Dragons and Zeref. Thrown in there for whatever reason.
Step 7: Guild wins.
Step 8: Go back to step 1 and repeat the whole process.