Sands of the West Chapter 2: Redfang
I don't know much about mightyena, just a bit about dark-types. they're vulnerable to fighting, fairy and bug-type, immune to psychic, resistant to ghost and other dark-types.
Kyurex (Pokemon): Part 28 - Altala - Fire of Death
Out of fear the water type released a bubble beam, but the umbreons reflexes helped the dark type out. "huh!" he moved his head to the side, charging another shadow ball. he loved this move...simple, and effective. "arrgh!!!"
Watcher of Arceus - The World of Arceus Side Stories 4, Norva 3
[i've gotten to the point i can track some dark types even... i refuse to let some humans pretend to hide from me.] norva stated firmly, turning back towards malcolm again. "norva."
Ember Tails side story - Firedog the First, pt3
Kyle simply gave a go-get-em huff and ran forward to take the first dark-type on, watching as his claws seemed to glow purple a little bit as he charged as well.
Curse of the MIghtyena
"looks like you have a way with dark types" grace said and giggled. "no kidding, say, where's luce?" "luce, oh, he left yesterday. said he wanted to get as far away from here as possible and took the first boat out" "that's odd...
Righting Your Wrongs (Chapter 6)
I can only assume that because dark types are the direct opposite to psychics that you already held such an ability.
Chapter 3: A Whisper of Shadows
dark types, especially liepards, thrived on deceit and trickery. but we didn't have time to argue. "look," i stated, "i know what you mean, but do we really have a choice but to listen to her?
Journey to another world ch40
I had to think fast as i remembered that jenavee had a disadvantage to dark type moves, i was unsure as to what attacks kit knew, but then there was rena. she of course knew fighting moves, which would be the type advantage here. ‘how about it rena?
The Human Species Ch. 90 - Forlorn (Epilogue of Episode XIII)
Relieved to hear she at least was not facing a dark-type, mew focused. although adapt with using every element, her psychic attacks were well-honed and far more powerful than anything else in her arsenal.
The Human Species Ch.118 - The Final Episode (Part 1)
Lucario wanted to respond, but was interrupted by a not-very-subtle twitch coming from the dark-type lying on the ground in front of them. zerobi's face had turned darker than usual.
A change for the Better
"a shadow pikachu is black and purple in color,and is a dark-type" "sounds dreadfull." "yes,very." "but do not defeat them,they may only get stronger with the weaker they get." arceus continued.
Sinori's Tale - Chapter Six
_her psychic ability didn't work on dark types!_ the umbreon's eyes widened as he thought through what that meant.