The Plague of Shadows appears similar to Plague Knight's boss form from the other campaigns, only it is completely black.
The Plague of Shadows appears after Plague Knight has defeated the Enchantress and completed the Ultimate Potion with her Essence. It is first revealed as the knight's shadowy outline cast on the stained-glass window. Lightning strikes and the shadow is separated from Plague Knight and projected behind him. It then starts moving on its own to fight Plague Knight.
Once defeated, the Plague of Shadows transforms into the Corrupted Essence.
The Plague of Shadows fights akin to Plague Knight in Shovel of Hope, except that the arena is made entirely of rising destructible blocks. Another important note is that Plague Knight's bombs can destroy the vats, which Shovel Knight could not do.
Alternatively, the Plague of Shadows can be defeated by remaining still for about 30-40 seconds, after which it speaks its line, ending the fight.
- "????: You are steadfast in your resolve... Maybe there's hope for us yet..."
- When the Plague of Shadows takes damage, the color cycling reveals the detail on its cloak and mask normally invisible due to its all black palette.
- This boss was possibly based off of a suggestion by twitter user Fireork recommending something similar to the X-Potion from The Candy Box 2.
- Although not clearly stated, this battle takes place in Plague Knight's mind. It can be interpreted as a mental test of his resolve by making him fight against himself.
- This would also fit considering this fight might've also been based off of the infamous Dark Link battle in Zelda II: The Adventure of Link due to the very close resemblance to the battle and how it also was a test.