Play Level 5-6: "Labyrinth", Level 5-7: "4Rooms", or Level 5-8: "Spilts". Each of those levels have two fast-moving crabs. Capture over 70% of the level, then remain idle until both crabs spawn. Quickly complete the level to earn the achievement.Easy "Underwater Legend" achievement
There are a few levels that are difficult to complete with a 3-star rank. One of them is Level 4-1: "Suprise". Start by killing the crab, then return to the starting position in the middle of the right side. Build a path very close to the lava. Enter the lava to kill yourself. After respawning, immediately go through the lava, and return to form a rectangle while you are invulnerable. Next, proceed safely to the left side of the screen while remaining in the middle position. Cut it when most of the enemies are in smaller sections. Then, complete the rest of the level quickly once it is safe.