Spike damage behavior

In Sonic the Hedgehog for the Sega Megadrive, spikes were originally presented to be as lethal to Sonic as falling down a pit or being crushed to death. When Sonic is injured by anything, including a set of spikes, he will become invulnerable, indicated by his sprite flashing the moment he touches the ground. However, if he lands on spikes, he will be harmed, regardless of whether he is flashing or not. This behavior is refered to as the Spike Bug.

The most frequently encountered (and argueably most annoying) occurance is when a number of spikes are placed together horizontally, causing death upon landing on the second spike after 'bouncing' off the first. This is not the only way to trigger it however; if Sonic jumps or falls into a set of spikes, he will still be harmed or die, even if flashing at the time of impact. This is cause of debate as to whether it was indeed a 'bug' or an intended feature.

First chronological evidence of removal was in Sonic 2 Beta 5.

Removal

• An official ROM hack was released as part of Sonic Mega Collection, called "JP2", where the bug was removed.
• drx actually created his own ROM hack before the release of Sonic Mega Collection, with the bug removed. He later released the source code, or rather instructions for removing the bug in an ASM file (disassembly). drx's bugfix has been implemented in Hivebrain's Sonic 1 Plus and South Island Adventure ROM hacks.
• FraGag made a tutorial on how to remove the bug, it is avaliable here.