Either of them could be done simply:
Luck: base level 0 (all classes), max level 25 (all classes):
A multiplier to your drop rates, 25 being the equivalent of what we currently get with active loot pots (loot pots don’t stack, they would be changed into candy of extreme luck to instamax luck).
So if you have maxed luck it would be like running with loot pots constantly on.
(I really dislike variable luck as a concept though, and that goes for loot pots too)
Resistance: increases with levelling, base and max levels vary by class
Reduces the duration of negative effects by 1% per point (so 50% duration if you have 50Res).
This would also kinda work as a “vit mod” concept. You can’t avoid negative effects completely but you lessen them if you’re maxed.
Other ideas off the top of my head:
Some kind of stamina/endurance stat could be introduced,
It’s kinda weird that our character stats never degrade. It could be that the 9th stat covers rate of decay.
So this would introduce every char has RNG chance of each stat decreasing daily.
But the RNG chance decreases in line with your maxedness of stamina. Max it and you get the minimal decrease.
Stamina’s not the right word for this idea but nothing better is coming to mind.
Quickness could be a stat, governing how fast we can swap items.
A very low stat would give you a second delay perhaps, max it and you get the instant time like now.
I don’t think this would be a very exciting concept for current Rotmg, but if we had additional item slots (a 2nd ring, or option for 2nd weapon in place of ability), this stat could be hugely important.
Some sort of pet-related stat could be the 9th.
So you need to max this stat to receive your full pet power. Leaving it at 0 you’d perhaps only get 50% of its ability power, or the pet’s effective level is reduced by 50%, increasing by 2pp per stat until max at 25 grants 100% of your pet.
Some type of stat for how much you’re affected by tiles ie. lava, that new ice, or slow terrain.
Something that multiplies the effect or duration of consumables (this could also be a Vitmod concept).
There really are a lot of possibilities!