This tutorial explains how you can easily learn Mighty Guard and White Wind in Final Fantasy VI.
To start off, make sure you have Relm and Strago on your team. Next, you should make sure you have the Hermes’ Sandals and Gale Hairpin equipped. You can buy Hermes’ Sandals in South Figaro when you are in the World of Ruin. The Gale Hairpin can be purchased at Nikeah.
You should also make sure you have at least two Remedies.
In the Configuration menu, set Battle Mode to Wait and Battle Speed to Very Slow. These will help prevent the Pepper and Land Ray from being defeated very quickly at the beginning of the fight before you even get a chance to act.
Once you are ready, head to the desert outside of Tzen. Here, you should eventually encounter the Pepper and Land Ray.
At the start of fight, use Remedy on Pepper and Land Ray. This will prevent them from being defeated as these enemies are start out with Sap status.
Next, you should use Relm’s Sketch ability to get the Pepper to perform White Wind and Land Ray to perform Mighty Guard. The Pepper may use White Wind on its own.
Using Sketch on Land Ray may result in another attack. In that case, you can try using Sketch again until you get the enemy to use Mighty Guard.
Once you see these two spells in action, defeat the enemies to learn them.