Golem

The Golem is a Hardmode boss. It is summoned by using a Lihzahrd Power Cell on the Lihzahrd Altar, which is found in the Lihzahrd.

The Golem has 2 phases and can be damaged in three places: the left fist, the right fist, or on the body just below the neckline (indicated by a glowing box and the damage indicator). The head is always invulnerable, but is important to avoid as it can deal damage by spitting fireballs or shooting lasers.

Important Note: The body hitbox is labeled as "Golem head" during Stage 1. When you transition into Stage 2, it will be labeled "Golem" while the head is detached and moving around the room.

In Stage 1, the Golem will shoot fireballs from the head, attack with the fists, and jump around; these abilities are timed and increase in frequency as each part takes more damage (when the fists are damaged, they will attack more often;  when the body is damaged, it will jump/shoot lasers/shoot fireballs more often). When the body reaches below half health, Golem will begin to shoot lasers from the head. This stage will last until the body of the Golem has taken full damage.

In Stage 2, the Golem's head will detach and fly above its body with increased speed while firing lasers at the player. It is identical to the previous stage without the fists.

Tips
Utilizing this same mechanic, occasionally the altar spawn in the tunnel just before the large temple room. Most, if not all, portions of the boss will be trapped in the brick around it, making the boss fight either extremely easy (If you have a weapon that passes through solid blocks) or impossible (if you don't).
 * Being one of the two bosses with a collision box for blocks (the other being King Slime), it is possible to beat Golem without incredibly good gear. While exploring the Lihzahrd Dungeon gather all the traps. Construct vertical pillars out of traps large enough for Golem but high enough for him to not get out on both sides of the altar. Finally line the ceiling with spike ball traps. After summoning Golem leave the enclosure and repeatedly activate traps to kill it.
 * You can place platforms in the room vertical wise and the Golem will spawn on top of the platforms making him easier to dodge and attack from below.
 * Vampire knives and Hallowed Armour or better make this fight extremely easy as standing right next to the Golem and holding down the mouse will outheal his damage, just move from under him when he jumps.
 * An easy method to kill the boss is to make some platforms above the altar so Golem will spawn on them, and then hide under a two block wide ceiling to avoid getting hit by fireballs and fists. Then, use the homing ability of Chlorophyte Bullets to your advantage by shooting around your "shield." The only thing you might have to worry about is the lasers of Golem is bound to shoot. With the proper gear, you can easily kill him before this becomes a problem.
 * Another way to kill it easily is to make a roof over an edge of the room, wait until he jumps on it, and start attacking him either with a mushroom spear or the chlorophyte swords. Since the floating mushrooms/ poison cloud go through walls, he cannot damage you until the second stage, and even then only the lasers will hit you. If you don't have that much defense, try getting a cross necklace for the longer invincibility time.
 * Megashark or Stynger ranged weapons can easily destroy this boss in record times. Though you can only get the Stynger from the Golem itself.
 * At low health, the Golem will begin firing lasers faster, so ensure that you have a suitable number of potions. It will also extend its fists more frequently. Try to destroy these first so that they don't become a problem later.
 * If you manage to get a Piranha Gun, it is very easy to slowly take out the Golem by hiding after shooting.
 * Sometimes your world will generate in such a way, where the golems head and body will spawn seperated, and the head will get stuck in the wall. Spears that can hit through walls are recommended in case of that situation.
 * Using the Bunny Cannon and a wall between you and the Golem, you can very easily take this boss out in a short amount of time. This takes about 50 explosive bunnies, just spam-click the cannon until it dies (tip: aim the cannon straight up and wait for the boss to stand on top of it).
 * The Golem only fires lasers during two parts of the fight, first when the head reaches 7500HP, but only if you move far enough for the head to turn to the side. After the head comes off and the body becomes vulnerable, the head will not shoot lasers until the body reaches 4000HP, but will then fire more rapidly as the Golem's health gets lower.
 * Another way to easily kill Golem is to make a roof above him with blocks that don't fall, like dirt blocks, and right before spawning him, place 2 clouds with the Nimbus Rod below the roof. Then you must rapidly move over the roof of blocks, from there, you can keep placing clouds as their rain will go through the blocks if they are close enough to them. A Spectre Armor set and a Cobalt, Obsidian or Ankh Shield will greatly help for this method.
 * The Death Sickle makes this fight trivial, simply building a wall between you and him and fire until it is dead, he will die far before the lasers inflict enough damage to matter.

Trivia

 * The Golem might be a reference to Kaos Karnage from Donkey Kong Country 3: Dixie Kong's Double Trouble