Playbooks
Swap Dbl Mug is a defensive set inside the Nickel formation, and that distinction matters: everything here is about presenting a five man pressure look from Nickel 4-2-5 personnel while only rushing three or four. The "Dbl Mug" tag means both linebackers walk down into the A gaps directly over the guards, and "Swap" flips the defensive end alignment so your RLE and RRE tags are inverted from the base Nickel Double A Gap sets. That swap is the whole point. It lets you put your best edge rusher on the offense's weaker protection side without motioning anyone, and it changes the loop and sim paths in plays like Blitz Loop 3, Blitz Loop 0, and Blitz Loop Sim 3 so the pressure comes from an angle the offense did not identify pre-snap.
Use the mug look on second and long or third and medium when the offense has to hold protection, then alternate between a true blitz (Mid Blitz, Hot Blitz 3, SS Dog 3) and a sim (Nickel Sim 2, SS Sim 2) from the identical shell so the same pre snap picture produces different results
Shade your coverage after the snap, not before: line up mugged, let the offense set protection, then bail one linebacker into the hook and user the other to the middle of the field so you are not leaving the seam uncovered
On Cover 1 Games and Cover 3 Sky, hot route your SLCB tag defender to handle the slot and user the free safety instead, since the slot is the primary hole in any mug based three deep shell
1 DT LB Loop and Redzone DT Drop are your goal line and short yardage answers because the DT drop clogs the A gap throw while the loop still threatens off the edge
Manually swap personnel into the RLE and RRE tags before you commit to this set, because the Swap alignment is only worth running if your best rusher is lined up against the weaker tackle