Prepare the instant pudding according to box directions. Place in refrigerator to set while you prep the other ingredients.
Wash, core, and chop apples into small bite-size pieces (you can toss the apples with a bit of lemon juice to prevent browning).
Chop Snickers bars into small chunks.
Layer the ingredients into a large trifle bowl. Begin with pudding, then cover with apples & Snickers. Repeat 1-2 more times. Then, top with a layer of Cool Whip and add some additional apple & candy pieces.
Notes
There's really no way you can go wrong with this--add additional layers, add Cool Whip to each layer, use a few more or a few less of the apples or Snickers bars...you could even add a little caramel drizzle. It keeps for a few days in the fridge, but it really is best served soon after making.