This crab was easy with lazortrons. I ran bullet in the middle 2 scorchers on each side of the landing area and the rest lazortrons behind. Hit level 70 with 32 attacks still left.
I was hoping to get Rain Makers again before Mega Crab but I hate that those are temporary even though it was originally in the Armory. The truth is not listed on Boom Beach Fandom.
I am not boosted and I beat round 40 without losing a single Lasertron. I use everspark Critter swarm and gunboat Critters, and I shock rocket launchers to prevent them from killing Critters. Nothing else is a concern because Critters protect the Lasertrons. Never flare to the Core.