I notice there's mention of a black robe of the archmagi in Magic Resistance, but (a) that item would give AC 16 with your Dodkong's DEX 13 (+1) or AC 17 if you used the (+2) Dexterity modifier it's listed as having for some reason.
That
Magic Resistance is missing a comma by the way, it should be:
Magic Resistance. While wearing its black robe of the archmagi, the Dodkong has advantage in saving throws against spells and other magical effects.
Also, its Spellcasting numbers are a point too high. Base 8 plus Proficiency +7, INT +6, archmage robes +2 makes a total of DC 23 not 24.
I'm guessing that some of these quirks are due to the custom rules you mentioned.
FYI, I made a stat block for the dodkong a few years back. The numbers are a bit off because it used my modified "5e epic rules," but it mostly works as is.
Since we've started on the
Special Traits section, I'll note that
Stone Glide gives its tremorsense which isn't mentioned in its
Senses. It should
Senses #2 tremorsense 60 ft. while burrowing, truesight 120 ft., passive Perception 20
However, I see no harm in just giving it normal tremorsense and use the standard wording for
Earth Glide:
Senses #3 tremorsense 60 ft., truesight 120 ft., passive Perception 20
Earth Glide #2. The Dodkong can burrow through nonmagical, unworked earth and stone. While doing so, the Dodkong doesn't disturb the material it moves through.
It doesn't change the Dodkong's combateffectiveness much since its truesight sees twice as far as its tremorsense, so when it's standing on the ground its vibration sense would only warns it against opponents that are underground.
Come to think of it, it's still not "standard wording" because as written the Dodkong can glide through worked material too, which'd make it:
Earth Glide #3. The Dodkong can burrow through nonmagical earth and stone. While doing so, the Dodkong doesn't disturb the material it moves through.