Boss

The Mayhem Boss is the boss obstacle in Smash Hit that is exclusive only for Mayhem Mode. It has a cannon-like thing that shoots small cubes at you. In order to defeat the boss you must hit all the colored sides. Some bosses, like Checkpoint 1's boss have a circle of walls around them. Checkpoint 2's boss is a double version of the Introductory stage's boss. Some of them have a "minion". Checkpoint 5's boss has a minion - a cube. The bosses also have a bit of "passive time". During that time they will expose their sides and this is your only chance that you can attack (assuming that the front side is disarmed). Below is a list of all the bosses and their appearance:

Appearance
Introductory stage: A single cube.

Checkpoint 1: A stronger version of the previous boss. (the circle of walls)

Checkpoint 2: Double version of the first boss.

Checkpoint 3: Triple cubes sticked together.

Checkpoint 4: Stronger version of the 4th boss*. (the circle of walls)

Checkpoint 5: The first boss to have a minion. (1-cube boss).

Checkpoint 6: Triple version of the first boss.

Checkpoint 7: Five cubes sticked together.

Checkpoint 8: Stronger version of the 8th boss**. (the circle of walls)

Checkpoint 9: Double version of the 4th boss*.

Checkpoint 10: 8th boss** with a minion. (1-cube boss)

Checkpoint 11:8th boss** with a minion. (3-cube boss)

* -Checkpoint 3's boss. **-Checkpoint 7's boss.

Rewards
This list shows how many balls each boss gives after death. Crystals are exchanged for balls here. (Checkpoints 0-4 and Checkpoint 11's bosses do not give rewards)

Checkpoint 5: 30 balls (6 octahedral crystals)

Checkpoint 6: 30 balls (6 octahedral crystals)

Checkpoint 7: 20 balls (2 3D stars)

Checkpoint 8: 18 balls (6 pyramid crystals)

Checkpoint 9: 20 balls (2 3D stars)

Checkpoint 10: 32 balls (4 pyramid crystals + 2 3D stars)

Tips

 * If you want to survive longer, collect ALL the rewards and the ones that are given before the boss arrives. They will be a vital part of your survival.
 * Because Checkpoint 11's boss doesn't give rewards after death, use the balls that you collected before the boss fight. There isn't much balls in Checkpoint Infinite (Endless Zone), because it is the hardest stage and after some time, things will get faster and the chance for you to miss valuable crystals will increase. Remember: crystals give you balls that you can use later on.