Magic Defense Down Application And Cap

While calculating out magic damage I noted some discrepancies of expected damage. I theorized that there may be a magic defense down cap. I did not find any information about it on bgwiki so I decided to do some testing. I intend to use this post as a reference when I add the information to a few pages on bgwiki. If anyone has additional information or questions on the subject please apply it here.

Magic Defense can be reduced in two ways; Geomancy and through blue magic or weaponskills.
The magic defense down from weaponskills and blue magic apply in the same reduction slot so only one will be active at a time. Geomancy applies in its own slot and stacks with the magic defense down from weaponskills or blue magic additively.

Magic defense down applied by weaponskills will overwrite each other and can be continuously applied.
When it comes to switching between BLU spells and weaponskills, the process of overwriting gets very complicated. In many cases, it will require the original magic defense down debuff to wear off before applying another. In situations where you are attempting to apply multiple different magic defense down spells or spells and weaponskills, you should personally test the application to see if they overwrite or require wear. A specific example that I found during testing is that I could not overwrite Shattersoul, Enervation or Benthic Typhoon with Tearing gust and Benthic Typhoon would overwrite tearing gust which would be less than ideal if the stronger magic defense down was desired. I do not know if this is always the case, so again, I encourage the people actually trying to do this to attempt it themselves.

Magic defense down caps when the enemy has 50 magic defense. To say this another way, enemy magic defense cannot be lowered below 50 magic defense. Examples;
If the enemy has 100 magic defense you can only reduce it by 50, leaving the enemy with 50 magic defense.
If the enemy has 150 magic defense you can only reduce it by 100, leaving the enemy with 50 magic defense.

So if you are fighting a standard (normal) mob with 100 magic defense and you have an Idris geomancer doing Malaise and applying Shattersoul then you are overcapping caping magic defense down (100-55=50 because that's the minimum magic defense). Consider using Malaise as the indi-spell so that blaze of glory and/or ecliptic attrition are actually providing a benefit to your geo-spell, but also remember that certain battlefields, monsters and content reduce the effectiveness of geomancy.

The maximum I was able to reduce magic defense was -120, with a bolstered malaise bubble and tearing gust on monsters with 170+ magic defense.

BST also has access to -25 Magic Defense Down from Swooping Zhivago and Fluffy Bredo. I'm curious to see how they interact with Weaponskills and BLU spells.

Thank you for the information, I had forgotten about the pets. I took out Attentive Ibuki and tested with Swooping Zhivago. It applies in the same spot as weaponskills and blue magic spells. I could not overwrite it with Shattersoul, enervation or tearing gust. Unfortunately, it would not overwrite a magic defense down already applied even if it was weaker.