The original Wildcat package at the University of Arkansas was run from 1 unbalanced formation.
What made the Wildcat so effective early on was the unbalanced formation with the QB flexed out at receiver. With the QB still on the field the defense couldn't tell if the offense was going to run the Wildcat or traditional 22 personnel formations and plays before they broke the huddle. Defenses initially had trouble dealing with the tackle over unbalanced, motion, and treating the QB as a receiver. Jet sweep, power, inside zone, and counter are the plays that made up the basic Wildcat attack. If defenses didn’t adjust to the unbalanced correctly you were out leveraged and the jet sweep got to the perimeter.
If the defense didn’t have enough bodies in the box or over played the jet sweep the power play would hit off the strong side edge.
When teams over shifted to the unbalanced to stop the sweep and power the counter play allowed the offense to exploit the undermanned weak side of the formation.
Inside zone was a complimentary play that could be run strong or weak and allowed the offense to have 3 double teams inside.
Video of the wildcat from Arkansas is available here. The first rule to playing defense is to get lined up and the Wildcat made that more difficult than traditional formations. By having the "QB" taking the direct snap the offense had a hat for a hat when blocking the core.
A great deal of the Wildcat’s success was tied to the formation, but what was initially the Wildcat’s strength became its Achilles heel. Because the Wildcat was being run with a RB at QB the threat of pass was extremely limited. Also Wildcat teams were lining up a QB at WR which further limited passing options. One solution is to limit the coverage to the QB. There is a low probability he is being thrown the ball so why cover him? The concept often includes bringing a blitzing corner (cowboy).
The concept is basically cover 2 with the corner blitzing instead of playing the flat. The SS should be able to handle the limited pass threat as the RB is unlikely to throw the hole shot on the sideline. The blitzing corner made running the jet sweep difficult and allowed the front to handle the plays in the core with minimal adjustment.
Another corner blitz solution was to bring the corner to the motion.
By blitzing the backside corner the defense is able to attack the running back and help eliminate the power, counter and inside zone plays. Using the backside corner in pressure allows more flexibility in the rest of the defense to adjust to the unbalanced and jet sweep.To take it a step further, you can blitz both corners (double cowboys).
Now there is a blitzer attacking both elements of the wildcat package (sweep and "QB"). The FS can key the H-back and help defend the weak side on counter and inside zone plays while staying front side on sweep and power. The TE is still a pass threat, although an unlikely one. One solution is to utilize the TCU cop concept and man the DE on the TE.
As defenses have evolved the Wildcat was forced to evolve or die. The issue was there wasn’t anywhere for the Wildcat to evolve. The pass game was never going to feature play action and boot, nor is it likely quick game, drop back pass, or screen will make an appearance. The run game was basically maxed out and defensive schemes were cranked up to attack the run. The only solution left was to adjust the formation. Unfortunately for the Razorbacks and the Miami Dolphins other formations have not had the same success as the original. I don't know if the Wildcat is gone for good, but I do know that offenses will have to find a solution to the corner blitz if it is going to make a comeback.