You can change in the item_db:
4262,Evil_Cloud_Hermit_Card,Cloud Hermit Card,6,20,,10,,,,,,,,136,,,,,{ bonus3 bAddMonsterDropItem,12029,RC_Plant,100; },{},{}
Change the "RC_Plant,100", 100 is equal to 10%.
4205,Mimic_Card,Mimic Card,6,20,,10,,,,,,,,136,,,,,{ bonus2 bAddMonsterDropItem,603,10; },{},{}
Change the ",10;", 10 is equal to 1%.
4206,Mystcase_Card,Myst Case Card,6,20,,10,,,,,,,,769,,,,,{ bonus2 bAddMonsterDropItem,644,30; },{},{}
And here you'll need change the ",30;", remember that 30 is equal to 3%.