Spike
Item
Spike was an upgrade planned for Sophia 3rd in Blaster Master but was cut for unknown reasons. It can be speculated that the upgrade would have given Sophia immunity to spikes and spiky surfaces, a functionality eventually realized by the Super Tires in Blaster Master: Overdrive.
Speculation[]
The existence of this upgrade implies that it was to be dropped by another boss, most likely the Plutonium Boss, and would give Sophia the needed immunity to pass on to a new section. The abundance of spikes in Area 8 supports this, as does the abrupt transition from the Plutonium Boss battle to the Underworld Lord in the finished game.