Go to Jolly's as either Banjo and Kazooie together or Kazooie alone. You'll need to only have one honeycomb left, so jump into the fire a bit to wear yourself down. Anyway, activate Jolly's jukebox and turn it off again (just so you're standing in the right place, you see). Fire a Clockwork Kazooie Egg behind you, move to a position a couple of steps behind Banjo's feet, and hold B. Voilá! The CWK Egg explodes and Banjo dies... but then he gets back up again to use the jukebox. Deactivate the jukebox, and voilá - Undead Banjo!