Playbooks

Doubles Y Off Nasty is the tightest of the Shotgun Doubles family, and that alignment detail is the whole point. You get two receivers split to each side, but the tight end (Y) is removed from the line and dropped into a nasty split, tucked just outside the tackle a yard off the ball. That off-ball placement means the Y is not covered up by the formation, so he is legal to release freely, he is easier to protect with pre-snap hot routes, and he almost always draws a linebacker or a strong safety instead of a true slot corner. Against 11 personnel base looks, that is the matchup you are hunting on every snap.
The nasty split also compresses one side of the field without going full bunch, which changes how the defense has to leverage the box. Defenses that stay in two-high have to decide whether to widen the flat player over the Y or keep him tight to the run fit, and that decision is what Double Post, Mtn Smash, and Mtn Slot Fades attack. On the other side you still have a clean isolated split end, which is why X Dagger and DBL Cross H-Choice hit so hard: the dig and the choice route work behind vacated middle-of-field zones while the outside receiver clears the top. Fork H Traffic and Pivot In Seams give you two of the better man beaters in the game from one look, and Cross Y Trail plus PA Y Cross let you drag the Y across the field against defenders who never win a horizontal chase.
Run game is where the set separates from spread-out Shotgun looks. Inside Zone, Outside Zone, Counter Y, and Tackle Trap all benefit from the Y being an extra gap-scheme piece who can arc, insert, or pull without being a covered lineman. Layer in the gadget shell with Zone Fake Jet, Jet Pass Fk Zone, Fake Jet HB Seam, and RPO Zone Read Bubble and you can run the same jet motion tell into a handoff, a seam shot, or a bubble read. Screens (HB Slip Screen, Mtn HB Cross Screen) punish the aggressive edge pressure this compressed look invites, which is why the set carries 3DRB, Gadget, and SLWR tags and plays best with a receiving back and a movement tight end.
Read the flat defender over the nasty split Y pre-snap. If he sits tight inside the tackle box, throw Cross Y Trail or PA Y Cross and let the Y run away from him. If he widens, get downhill with Inside Zone or Counter Y into the vacated gap.
On single-high looks use Double Post or Mtn Slot Fades. On two-high looks flip to X Dagger and DBL Cross H-Choice so you are always attacking the shell the defense declares.
Use jet motion from Zone Fake Jet or RPO Zone Read Bubble on early downs just to gather information, then run Fake Jet HB Seam later in the same series once the safety starts cheating to the motion side.
Third and medium with a 3DRB on the field is your Snag HB Wheel and Fork H Traffic window: the snag holds the flat defender while the wheel and the traffic route work above and behind him.
Against interior pressure, hot route the running back to protect and hit Pivot In Seams or a quick slant off the isolated split end instead of forcing the deeper Mtn Smash concept.