Was beginning to start breeding Pokemon capable of mega evolution and I remember seeing that gallade can learn shadow sneak via breeding,jus wanted to know how I can do so from people who know how to or have done so already
Try to get a female Ralts on Route 102. A female Kirlia or a Gardevoir could also work. If you have a Ditto, you can try breeding it with Gallade to get a female Ralts.
Catch a male Shuppet or a male Duskull (their evolutions also work). Both of them are available at Mt. Pyre. Have Duskull learn Shadow Sneak at level 17, while Shuppet learns it at level 13. You'd have to go to the Move Reminder in Fallarbor Town (northwestern-most house) to relearn Shadow Sneak (if it already learned Shadow Sneak, you don't need to do it). In order to get a Heart Scale for the Move Relearner, find it on wild Luvdisc (check locations).
When you got that done, breed the Ralts and Shuppet / Duskull together at the Day Care center on Route 117 or on the Battle Resort.
Finally, hatch the egg and you now have a Ralts with Shadow Sneak! You can evolve it into a Kirlia, then a Gallade.
Step 2 can be skipped if you already have any of the Pokemon in this link (it has to be a male though) that has learned Shadow Sneak. Just use this Pokemon to breed with the female Ralts.
Hope I helped!
Source: Experience, Above Links