You can attempt to make some Surfin Merkins, and anything that resembles a mole crab. The merkins are the pink ones, I use different types of spun fox fur on these and mallard flanks tied in "spoon" style to imitate the casing on the crabs. Good luck
I haven't fished Mazatlan, but I have fished the surf elsewhere in mexico and have heard the fishing is similar in Mazatlan. Large baitfish patterns that imitate the local sardines are what most folks use. I tie my own so I don't know any sources for flies although I have bought flies from Baja Anglers in Cabo when I was there. Flies like deceivers, surf candy, and flies of that sort and profile in tan or white with green or blue backs have done well for me.
Throw a few Clousers in. They travel well - work almost anywhere in the world. Just vary size of hook and eye. Another fly I've used is Trey Coombs Sea Habit Bucktail. He varies the colours for different baitfish and there is a small sardine pattern and an anchovy pattern. They are commercial patterns so you could purchase a few, or of course tie your own. Dressings are in trey's book called "Bluewater Fly Fishing". I found that patterns tied on 1/0-3/0 hooks weren't bad to cast and almost everything seems to like them. I really liked the blue, green and white ones.
Haven't been exactly where you are going, but these two patterns have worked well for me on salt water anywhere I have fished them.
A forum community dedicated to Spey casting, fishing, flies, and enthusiasts. Come join the discussion about trails, licenses, fishing, game laws, styles, reviews, optics, accessories, classifieds, and more!