On the patch notes...

Whalaqee Totems

Certain blue magic spells can be acquired via Whalaqee Totems.

To obtain these items, complete the blue mage quest "Blue Leading the Blue" and certain achievements, then speak to Wayward Gaheel Ja in Ul'dah - Steps of Thal (X:12.5 Y:12.9).
I would assume abilities like Mighty Guard that aren't on any (ARR) enemies, are obtained that way...




And for a few abilities on the list, enemies that do have them...

White Wind, Enkidu at the Battle in the Big Keep, he casts it on Gilgamesh on a regular basis.

Aqua Breath, pretty sure it's on Ultros in The Dragon's Neck, you need to get hit by it as a kappa.

Diamondback, the second boss in Stone Vigil (Hard), Cuca Fera. It's the ability that makes him immune to damage and reflect the cannons.

Acorn Bomb, pretty sure either generic Treant enemies, or at least Amdapor Keep (Hard)