1. BACK TO BASICS
I'm not sure if you're aware that there are two kinds of Elemental resistance on Ragnarok Online. One has it from armor cards, eg. Dokebi, Ghostring, Angeling, etc. and the other are from equipment-based cards (sorry I don't know how else to categorize them) like Leib Olmai, Marse, Jakk, etc.
This you should also know that Elemental Armor Cards do not stack with Elemental Equipment Cards. The reduction has it that it takes into account the Elemental Armor Card's resistance, only then the Equipment ones are calculated (correct me if I'm wrong on this). This means that... If you're using an Angeling Card in your armor, and u're using 2 Jakk Cards in your Garment, the maths IS NOT 25% + 60% giving a total of 85%... NO!
But rather, the real scenario is that the amount of raw damage (not deducted by any resistance), you multiply it by 75% (that's the amount of damage you'll still take from Fire sources), then the value u get you multiply it by another 40%, that's the final amount of damage you'll be taking from Fire sources after taking into account the Jakk cards.
Having that taken into consideration, if you were to use an Angeling card, you are also imposed a penalty of taking an additional 25% dmg from Shadow/Dark sources. However...
2. SHR GAMEPLAY
Now when the above basics are applied to a SHR server, it becomes rather... sensitive primarily because of the 4 slots customization, and if that's not enough, you have custom elemental resists offered on various gears as well.
Therefore, it has become quite possible for a player to have up to 8-9 elemental resistance. What happened is this that... if you were to use an Angeling card in your armor, AND if you have 100% Shadow resistance, it creates a condition whereby you do not get penalized from Shadow sources anymore, simply because you have the 100% Shadow resistance on-top of the Angeling armor that you have... And this is wrong.
Therefore, as it only affects gears that offer high Holy resistance, particularly The One Armor and Odin's Armor, if these armors were to be paired with an Angeling, Bathory or Evil Druid, the elemental armor penalties are enforced by:
In the case of THE ONE or ODIN armor paired with:
1. Angeling Card:
-15% Shadow/Dark resistance.
2. Bathory Card:
-15% Holy resistance.
3. Evil Druid Card:
-30% Holy resistance.
-15% Fire resistance.
So yea... It had to be done... I personally don't believe in 8-9 elemental resist characters though it could be quite "fun" to have one...