Magic Guard isn't currently programmed to ignore Sticky Barb for some reason:
252 SpA Choice Specs Dragapult Shadow Ball vs. 252 HP / 0 SpD Clefable: 178-211 (45.1 - 53.5%) --
guaranteed 2HKO after Sticky Barb damage
There doesn't appear to be any info regarding the interaction with MG on the Showdown/Smogon dexes, but MG users seem to be immune in battles on Showdown and Bulbapedia says that it is ignored by Magic Guard, so I figure it's just an unintended omission.
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Also lmk if part of this is an actual mechanic that I don't know about, but the damage calc will ALWAYS give Zacian, Zamazenta, Zacian-C, and Zanazenta-C +1 regardless of whether they have Intreped Sword/Dauntless Shield or not and, regardless of whether this is supposed to happen, Dauntless currently does not work correctly.
To check whether this was just a bug that arises when removing the ability, I manually edited Cobalion's stats to match those of Zamazenta-C and had the two use Close Combat on each other and non-DS Zama-C had the same damage calc as Cobalion:
252+ Atk Zamazenta-Crowned Close Combat vs. +1 64 HP / 0 Def Cobalion: 312-368 (91.4 - 107.9%) -- 50% chance to OHKO
252+ Atk Cobalion Close Combat vs. +1 64 HP / 0 Def Zamazenta-Crowned: 312-368 (91.4 - 107.9%) -- 50% chance to OHKO
I then checked against a blank set Zama-C and it appears the +1 is still said "vs +1 Zamazenta-Crowned" even when Dauntless Shield wasn't on it in the first place:
0 Atk Zamazenta-Crowned Close Combat vs. +1 0 HP / 0 Def Cobalion: 236-278 (72.6 - 85.5%) -- guaranteed 2HKO
0 Atk Cobalion Close Combat vs. +1 0 HP / 0 Def Zamazenta-Crowned: 236-278 (72.6 - 85.5%) -- guaranteed 2HKO
I tried going to Aboma and then back to Zama in case it was just a bug going from one Zac set to another and it persisted.
I then removed Dauntless Shield from the Cobalion and checked the Zama CC calc again. The +1 vanished from the text but the damage stayed the same:
0 Atk Zamazenta-Crowned Close Combat vs. 0 HP / 0 Def Cobalion: 236-278 (72.6 - 85.5%) -- guaranteed 2HKO
I then manually applied +1 Def and the damage decreased as expected:
0 Atk Zamazenta-Crowned Close Combat vs. +1 0 HP / 0 Def Cobalion: 158-188 (48.6 - 57.8%) -- 95.7% chance to 2HKO
Finally, I checked regular Zamazenta and, like Zama-C, the +1 text without any real boost was automatically applied regardless of whether it had Dauntless Shield or not.
TL;DR:
- Zamazenta and Zamazenta-C have been hard-coded to have the effect of Dauntless Shield applied to the calc text but the output is otherwise unaffected
- Dauntless Shield automatically applies the +1 calc text but the boost isn't ever substituted into the output formula
I've not done a comparison with a fake Zacian/Zacian-C for Intreped Sword, but I assume it's been implemented in the same way considering the same text bug appears for both Zacs regardless of whether they have Intreped Sword or not. The damage seems to work correctly for these though.