Couple of quick thoughts:
Dagger Master
I agress the attribute increase should be STR or DEX. I also agree that turning a 1 into 10 doesn't sit right. Why should rolling a Fumble suddenly get you an Average hit roll when a 2-9 doesn't? Doesn't make any mechanical sense. Something more balanced would be allowing a 1 to be re-rolled once per short rest, OR simply state that a 1 is not considred a Fumble (effectively being the same as rolling a 2).
Mace/Maul Master
Advantage vs. Natural Armor doesn't make sense to me. In most cases I can think of natural armor would actually be best against blunt and slashing weapons. Simarly against heavy armor (with the exception of helms). Piercing weapons would be the type to do the best against these armors. However, overall, Mace and Maul Mastery just kind of fall flat for me. If anything I would combine the two into a single feat that affects all bludgeoning weapons more akin to Great Weapon Master than Crossbow Master. The question you need to ask is what makes these weapons "special"? For instance polearms' trick is they have two end to fight with. What are blunt weapons best at? Why would you choose one over other weapon types? Historically blunt weapons were either more commonly available weapon types or were specfically designed for the purpse of impact. Against heavy armor specifically they were designed as helm/skull crushers or if really excelling in their use, busting up the joints in armor. That said, I'd focus on a single feat for use with all "clubbing" style weapons which for D&D terms is basically any blunt weapon. Maybe something like:
* Increase STR by 1 to max 20.
* On your turn, when you score a critical hit with a blunt melee weapon, the target is also stunned until the end of its next turn in addition to the effects of a normal critical hit.
Undead Hunter
This doesn't feel quite right to me either. Advantage vs paralyzation doesn't speak undead to me. Yes Some undead paralyze but its only a select few. Also the AC bonus doesn't make sense to me. I can understand the concept but only for against mook undead and this ability isn't undead specific, its against ALL foes which is technically too powerful, almost a feat unto itself IMHO. Looking at the Mage Slayer, the feat is useful for more than just "mages" true, but its effectively been boiled down to the concept that what a mage slayer needs is effects against magic because that what makes a "mage". So the question becomes "what makes undead uniquely different from other foes"? Well basically that is the Undead Type as its really the only common element to all undead. What else is pretty common and that could be used to create feat specific abilities?
* Overcome an undead's DR/immunity from nonmagical weapons, thus your melee attacks act as magical
* Gaining advantage on Saving Throw rolls vs undead attacks
* Doing additional Radiant damage on attacks (as undead arent immune)
Or model after mage slayer...
* When an undead creature within 5 feet of you uses an attack action, you can use your reaction to make a melee weapon attack against that creature
JMHO. YMMV.