OVERWHELM

The Twin Lizards are located in the top right of the map. After breaking the crystal container, you must fight and defeat both of the Twin Lizards to earn the ROCK achievement.

Luckily, you can turn on all the assists in setting which will not interfere with your achievement unlocking so definitely check them all!

Strategy


After awhile of evading and shooting, you'll take down both Twin Lizards (signified by it stopping and then bursting into white energy). The achievement will pop after defeating it.

Extra Tips - Order of Bosses to fight
1. Kraken (Bottom right)
2. Lizards (Top right)
3. Worm (Bottom middle)
4. Skullbat (Top left)
5. Bush Spider (Bottom left) - Easiest to fight for it's ultimate form.

Prior to starting the game make sure you throw on all of the assist options as they do NOT disable achievements. You can find these under Options->Difficulty

Twin Lizards is the boss protecting the crystal located on the top right. The lizards often stick very close to each other but will also try sync to create a sort of pincer attack. Much like the other bosses however, there isn't much to this: keep a safe distance and hold down the fire button to max out your DPS.

A video of the fight (credit to iamoverthisusername) is shown below with a solid strategy of keeping distance showcased.