normal card drop = 1 = 0,01% drop chance
= item_rate_card: 100
item_rate_card: 1000 = 0,10% drop chance
item_rate_card: 10000 = 1,00% drop chance
item_rate_card: 100000 = 10,00% drop chance
item_rate_card: 1000000 = 100,00% drop chance
Just set your item_rate_card to
item_rate_card: 200000 and you will have 20% card drop
and set
item_rate_card_boss: 10000 for 1 %
For your gloom card to have 10% just edit the dropchance 1 to 10.
Or did you mean 0,10% for gloom?
That way you would have to set item_rate_card_boss: to 1000 = 0,10% and edit all the other card drop to match 1%.