Keeping the Crusher centered in the Builder Base helps protect it from ranged troops.
Use Push Traps to push ranged units into the Crusher.
You can make an opening in your village using Walls to lure ground troops so they can push them into the Crusher. The troops will not want to break the wall so they will go through the gap.
You can put a Guard Post near a Crusher so the Guard Post troops lure your opponent's troops into the Crusher to get crushed.
Put good, short ranged defenses, such as the Double Cannon behind the Crusher (more towards the center of the base, where your opponent's troops will have to go through the Crusher to get to it) to protect it.
Try to avoid putting Crushers by walls as they cannot crush the melee over them , allowing the ranged units more time to destroy the Crusher before it can crush the melee units.
Try to put Crushers near your Firecrackers and Air Bombs to protect them from the Skeletons of the Drop Ship, as they will not be able to destroy the Crusher easily and it will stall the Drop Ships, therefore your Firecrackers and Air Bombs have plenty of time to take it out.
Offensive Strategy
The Boxer Giant's Power Punch ability can destroy a Crusher if there are enough giants at once.
Use air troops to take down the Crusher if using a swarm attack. This is only for unprotected Crushers - watch out for Firecrackers, Air Bombs and the Archer in the Guard Post!
To avoid a luring technique, as explained above, use Bombers to destroy walls and create another opening into a base away from the Crusher.
The Battle Machine can take out the Crusher before it does massive damage to units. However, with the help of other defenses, the battle machine will likely be at low hitpoints or taken out by the Crusher, even if the ability, Electric Hammer, is used.
You can take advantage of the Crusher's cooldown time to make it crush a few Raged Barbarian then swarming it with multiple Raged Barbarians to take it down before it has chance to crush the rest of the Raged Barbarians again. This technique requires precise timing and can ruin your attack if not executed correctly.
Upgrade Differences
The Crusher undergoes significant visual differences at levels 3, 4, 7, and 8.
At level 1, the Crusher looks like a mossy stone attached to a large screw emerging from a hole in the ground.
At level 2, the stone has wooden planks attached to its sides. The bolt at the top turns into metal one.
At level 3, the crushing stone becomes larger, the planks are replaced with ropes, the bolt becomes shaped like a hexagon, and the moss disappears. Some stones appear around the crushing platform.
At level 4, the ropes are replaced with metal blue bands.
At level 5, the crushing stone becomes even larger, the bolt at the top of the stone becomes gold, the hole receives a golden fitting, and the crushing area is now completely surrounded by stone.
At level 6, the metal bands are now gold and the crushing stone is slightly darker.
At level 7, the metal bands disappear and the crushing stone turns black. An extra bolt also appears at the top.
At level 8, the bolt grows in size and the top of the crusher gains gold plates. The sides of the crushers gain spikes.
At level 9, the crushing stone gains golden plating at each corner and there seems to be cracks within it.
Trivia
The Crusher is the only defensive building (from both bases) that doesn't shoot any kind of projectiles.
Supercell was going to add a 2nd Crusher to Builder Hall level 7, but then they decided to add it at Builder Hall level 6.
On 9/29/2017, the Crusher could no longer hit over walls, even if units are within its range.
Icon Descriptions
Tapping this icon displays information about the Crusher, such as Level, Damage Per Second, Hitpoints, Range, Damage Type and Targets.
Tapping this icon begins upgrading the Crusher to the next level, if you have enough resources and a free Master Builder or O.T.T.O. When the Crusher is at maximum level, this icon is not shown.
Tapping this icon instantly upgrades the Crusher to the next level, at the cost of one Hammer of Building if you have one. When the Crusher is at maximum level, this icon is not shown.
Tapping this icon, which is displayed only while an upgrade is in progress, instantly finishes that upgrade at the cost of the displayed number of Gems.
Tapping this icon, which is displayed only while an upgrade is in progress, instantly finishes that upgrade at the cost of one Book of Building. This icon is only shown if you have at least one Book of Building.
Tapping this icon, which is displayed only while an upgrade is in progress, instantly finishes that upgrade at the cost of one Book of Everything. This icon is only shown if you have at least one Book of Everything but do not have a Book of Building.
Tapping this icon, which is displayed only while an upgrade is in progress, cancels the current upgrade and refunds half of the upgrade cost.
*Exact value as derived from game files. In-game, this is stated as being 2 tiles.
**The splash radius is always centered on the Crusher, unlike most splash defenses whose splash radius centers on the location where the projectile hits.
