Iron ball

The spiked ball (トゲボール) also known as the Iron Ball (鉄球) is an obstacle that appears in the Sonic the Hedgehog series. It is a variant of the more common Spikes, being a metal sphere covered in harmful spikes.

Description
Spiked balls have maintained an overall consistent design over the course of the Sonic series, being heavy gray/black spheres that are covered in white/gray spikes. The dimensions of the spiked balls tends to vary from game to game though.

In gameplay, when a playable character physically touches a spiked ball, they will receive damage. As such, they usually serve as obstacles that are placed along the player's way in the levels. Occasionally, the spiked balls will be stationary. In different games however, they tend to be attached to chains or other devices that causes them to swing around. On other occasions, the spiked balls will be moving around in midair on their own as well.

In later games such as Sonic Unleashed, Sonic and the Black Knight and Sonic Generations, spike balls are usually set just on, or embedded in the ground.

Sonic the Hedgehog (1991)
These variants are first seen in the 16-bit version of Sonic the Hedgehog, as spiked balls spin around in certain sections of Spring Yard Zone. Smaller spike balls appear swinging around in Labyrinth Zone, while larger spike balls appear swinging back and forth in the second act of Scrap Brain Zone.

Sonic the Hedgehog 2
Black, slow-moving spike balls orbit platforms in Sonic the Hedgehog 2 's Mystic Cave Zone.

Sonic the Hedgehog 3 & Knuckles
In Sonic the Hedgehog 3 and Sonic & Knuckles, there are specific large spike balls that block the player's path using different methods, such as swinging around either vertically or horizontally in Marble Garden Zone (dependent on the pole it is attached to), or even rotating to the player's neck at one point in Lava Reef Zone.

Sonic 3D Blast
They make some appearance sin Sonic 3D Blast. Various spiked balls are found in Rusty Ruin Zone, including unique ones that appear like statues built into the ground. Also, during the Green Grove Zone boss, Eggman is equipped with a spiked ball that he attempts to drop on Sonic. It bounces a few times when dropped.

Sonic Adventure
In Sonic Adventure and Sonic Adventure DX: Director's Cut, spike balls became slightly more common obstacles. While some swing around on chains, there are also some that simply float midair. Some of the floating ones will also periodically slam into the ground.

Sonic Adventure 2
Spiked balls make another appearance in Sonic Adventure 2 and it's remake, Sonic Adventure 2: Battle. Much like the preceding game they can either swinging around or simply floating midair.

Sonic Advance
In Sonic Advance, spiked balls appear during Casino Paradise's boss, Egg Ball, appearing from the same tubes Eggman is flying through. They also appear as regular obstacles in levels, such as Angel Island Zone.

Sonic Advance 3
Spiked balls appear in Sonic Advance 3 as part of the Egg Chaser boss. Eggman will occasionally flip the machine over and launch a mace at the player.

Sonic Heroes
They reappear in Sonic Heroes as standard obstacles.

Sonic Rush
The Egg Scarab in Sonic Rush attacks the player with spiked balls. However, the spikes will occasionally retract, at which point the player can Spin Jump into the ball to send it rolling back towards the boss. As long as the Scarab's claw are facing away from the ball at this point, it'll get hit and take damage, otherwise it can easily catch it.

Sonic the Hedgehog (2006)
In Sonic the Hedgehog (2006), Silver can grab these with his Telekinesis ability and utilize them to destroy enemies or other obstacles. Some spike balls will roll down inclines in Dusty Desert or Kingdom Valley.

Sonic and the Secret Rings
Spiked balls appear as common obstacles in Sonic and the Secret Rings. They either move around in the air, or are placed on or embedded into the ground. At the end of Sand Oasis's second mission, some spiked balls will get in the player's way by rolling down the hill.

Sonic and the Black Knight
They reappear in Sonic and the Black Knight, acting as simple obstacles.

Sonic Unleashed
They reappear in Sonic Unleashed, acting as standard obstacles. In some of the daytime Acts, they will appear midair and require the player to time homing attacks carefully so Sonic doesn't smash into them.

Sonic Colors
Spiked balls appear as obstacles in Sonic Colors. They will also be dropped by the Frigate Orcan and Frigate Skullian bosses. Also, if the player gets a non-beneficial line-up of symbols on the slot machine in the Sonic Simulator, theen the slot machine will release spiked balls.

Sonic Generations
They appear in Sonic Generations, acting as obstacles in both Classic and Modern stages such as Seaside Hill.

Sonic Lost World
They reappear as standard obstacles in Sonic Lost World. They appear most frequently in auto running sections, either embedded in the ground as in Desert Ruins Zone 2, or simply floating and possibly even moving around the platforms.

Sonic Runners
Spiked balls appear occasionally as obstacles in Sonic Runners. Dr. Eggman will also drop spiked balls in the Iron Ball Eggmobile fight.

Sonic Runners Adventure
Spiked balls play the same role in Sonic Runners Adventure as they do in it's predecessor, up to and including being dropped by Eggman in a boss fight.

Sonic Mania
In Sonic Mania, and its expansion Sonic Mania Plus, spiked balls appear as regular obstacles, particularly in Flying Battery and Lava Reef. They appear both on their own (including the variants in Flying Battery that are periodically raised by the Zone's electromagnets) and swinging on chains. Heavy Rider wields a spiked ball that she swings around on a chain.

Sonic Forces
They reappear once again in Sonic Forces. They can be seen both floating (stationary or not) and swinging around on chains. During the first boss fight with Infinite, taking damage from his cubes can potentially lead to a virtual reality with spiked balls to avoid.