How do you beat the void overlord in primary

Once you go to Floor 10, 20 or 30, there is a gate to open and there are three spike puddles. These are where the boss comes out. To kill him, wait for a blue target and put an ice block there and step backward to the puddle away from the boss. He will hit the ice and get frostbitten. Quickly switch to red and burn him. He will get hurt. You'll have to repeat this process three times to kill him. If no blue target appears or just an arm, then be yellow and be invisible until it's safe.