Difficulty spike
Also said as Difficulty wall, Brick wall
One point where a game suddenly gets much harder than what came before, and then often eases off again.
A spike is where players quit. Those who could have finished the game hit a stretch that nothing prepared them for, and there is no reason to come back. A deliberate spike needs warning and a good reason.
Say it
“Level 6 is a spike: playtesters pass 1 to 5 in two tries each, then take twenty on 6. Move the laser section to level 9 and add a practice room before it.”
Where you’ve seen it
Battletoads on the NES is the famous case: its third level, the Turbo Tunnel, asks for split-second memorised reactions on a speeder bike, and many players never saw what came after it.
Not to be confused with skill gate
A spike is any sudden jump, usually an accident. A skill gate is a deliberate check on one skill the game has already been teaching.