Typically either Superheavy Samurai or Aromage are F2P decks That get mentioned.
I play Metaphys, because they work really well in the meta. The only things you need for them are to go through the box once, although 2 Dimension is perfectly acceptable, typically have someone with Heavy Starter or Grit, and 2 Kiteroid from the Trader.
Lunalight is actually quite decent pick for the KC cup, you'll have a lower win ratio but you get more duels out and therefore more points. Stuff like super heavy samurai and aromage just give away free wins in stage 2.
took long time to build, but if you want have fun getting opponent stress, heres my decklist. 1st deck increasing Lp 187k in 20 round. kiteroid x2, griggle x3, kiseitai x3, mistic box x3, the golden apple x3, enchanted javelin x3, nutrien z x3, jar of avarice x2, hidden spellbook x1. skills duel standby tea gardner.
2nd decks for farming 8k points x3 rewards, main star is tyranno infernity x3