Guncraft Blocked and Loaded

First you need to rank up a bit to unlock Lava Survival game mode. A good way to rank up is to do the "Capture 100 flags" achievement against a 2nd controller. It unlocks near the beginning, before rank 15.

Then, when you have Lava Survival unlocked, play a match of it on the map Face-off against a 2nd controller or player. There will be 2 helicopters located inside the base. Go to the helicopter and start flying with the 2nd controller. Go to the outside bridge where the lava is rising. Then, shoot the helicopter down with your weapon of choice, when the helicopter is destroyed, the 2nd player will turn into an ice block and fall to the lava, unlocking the achievement.