I've never gotten a usmash kill in my life... usmash is such a horrible move. I kill most frequently with fair (OOS, baited air dodges, just because), rest (baiting air dodges rolls and spot dodges, OOS, drillrest, drillerstOOS, punishing bad commitments), and roll out(punish some landings, baited grabs and spot dodges, sheild pokes, hard reads), dash attack (OOS, anti air, punish landiing) that order.
I've never looked into dacus OOS though..... maybe a strong punisher for some moves.
I spam bair dair jab and grabs to keep my fair and dash attack fresh.
Dair is prob jiggs best move IMO, really good damage, very very safe o nsheild. fast. auto cancels, tons of time to hit confirm. you can pick sides to avoid sheild grabs and some OOS options. characters like marth, DK, and bowser can 100% get out.
I'm also in love with Bair's relatively low cool down, since if people spot dodge it you can follow up with things because of you low fall speed. don't think any other character can really do that...
jig's jab and ftilt are some of her best ground options. start up isnt amazing, but relatively low cool down on both (jab beast spot dodges) you don't get punishes hard on sheild. jab can lead into neat grab or dair mix ups, ftilt has surprizing range and a good knock back tragectory.
dsmash is the best taunt in the game.