Big Guardians like Stalkers, Skywatchers and Turrets can only shoot lasers at you - it’s their only attack. These lasers have two hitboxes:

• The beam deals 52 points “physical” damage. 8 of that are fix, 44 of that can be reduced.

• The explosion deals 6 points “fire” damage.^[1]

Every 1 point of armor defense reduces damage by 1 point (one quarter heart), but armor defense does nothing against fire damage. Additionally, you can not reduce the physical damage to less than 8 points by ANY means - no matter what you wear and how strong it is, you will recieve at least 8 points of damage. The only part of the physical damage that CAN be reduced is 52-8= 44 points.

The only thing that shields Link against the fire damage is the “Fireproof” armor set bonus from the Flamebreaker Armor. ONLY the set bonus - it does not work with regular Flame Res from elixirs or the “base” effect of the un-upgraded Flamebreaker Armor. If you wear literally anything else, you will recieve 6 points of fire damage.

Now for the “Guardian Resist” bonus, that stuff reduces the physical part of the damage by an additional 20% / 30% / 50% depending on the level, but still does nothing against the fire damage and it’s still not able to reduce the total damage below at least 8 points. And the bonus is calculated after everything else.

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Some examples:

 

Example 1: You’re wearing the complete Ancient Set but none of the pieces are upgraded (armor rating 12 points total). This would normally reduce the damage you take from physical attacks by 12 points (3 hearts). The additional 50% will make it so that the damage gets reduced by 18 points instead (4,5 hearts). The difference is literally one and a half heart then. (And the added fire damage is still 6 points on top of that no matter what)

• To elaborate further: if you get shot by a Guardian while having 12 points of defense, you will recieve 8 points of guaranteed physical damage, 6 points of fire damage, and 44-12 = 32 reduced physical damage for a total of 8+6+32 = 46 damage (11,5 hearts). With the added 50% Guardian Resist bonus you will “only” recieve 10 hearts of damage. Doesn’t make that much of a difference if you have less than 11 heart containers and the shot outright kills you in both cases anyway.

Example 2: You’re wearing the full Ancient Set and all pieces are upgraded to the max already, for 84 defense total. This would normally reduce the damage you take by a whooping 84 points, but the beam doesn’t even do that much. You can only reduce 44 points of that and then you’ll recieve the guaranteed 8 points of physical damage and the 6 points fire damage anyway, so the resist bonus makes zero difference.

• To elaborate further: You get shot by a Guardian while wearing this setup. You will recieve 8 points of guaranteed physical damage, 6 points of fire damage and the other 44 points of the beam get eaten up completely by the physical defense of the armor, so your total is 8+6+0 = 14 points (3,5 hearts). The triple Guardian Resist would now theoretically boost the 84 points of defense to a whooping 126 points, but it doesn’t matter anyway as you already blocked the 44 points that CAN be blocked. The “damage formula” is still 8+6+0 then. The third number never goes below zero.

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So in conclusion …

 

If your armor has at least 44 defense, it will already fully reduce the part of the physical damage that can be reduced. In that case, it simply doesn’t matter anymore whether an additional boost would theoretically reduce the damage further or how much higher your armor rating actually is.

Funnily enough, the Flamebreaker Armor can actually be more effective in this case, as it is able to reduce the full 44 physical points (it can have up to 60 defense) AND the full fire damage, so you’ll only recieve the 8 points of physical damage (2 hearts).

This does not mean that the Ancient Armor Set as a whole is useless - on the contrary. It offers one of the highest defense ratings in the game, and the additional 80% damage boost from the “Ancient Proficiency” set bonus even stack with regular “Attack Up” from food, so you can deal massive damage this way. But the “base effect” of one level Guardian Resist per piece makes only a tiny difference early game, and no difference at all during the late-game stage.

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1. Enemy Statistics by OneOf99 @ gamefaqs ↩︎