Uhh...
Fsmash kills, Uair, bair, nair, usmash, utilt, ftilt, all kill. I would say dsmash but it wont likely have use as Jiggs will be in the air mostly.
Fair likely wont be a good ko move cause...well...we spam it.
Dancing blade can even kill Jiggs (especially if we miss one of the hits), as long as its fresh.
What kill moves does Jiggs have on Marth that dont require Marth whiffing a dsmash to connect with lol. Im always hearing rest, but that move is wayyy to risky to be brought up in a Matchup discussion and if it misses, Jiggs is dead.
The best attribute to Jiggs is that you play so few of them, you might not know how to handle her.