Spiker, called Tsun-tsun (ツンツン) in the Japanese manual, is a badnik from the 16-bit version of Sonic the Hedgehog 2 found in Hill Top Zone. It is a little red insect with a large spike on its head. This enemy is often found walking along the ground, although it can also be seen on the ceiling of caves. Regardless of its location, its attack is the same - As Sonic approaches, it fires its spike upwards if it is on the ground, or downward if it is on the ceiling. The spike is easy to dodge and once it has been fired the enemy is mostly harmless. Just spin attack to destroy it.
The Sonic 3 enemy Turbo Spiker is evidently an improved model of this Spiker; it moves faster and fires its spike at a slight angle, but its behavior is otherwise identical.