You've fought your way into the evil lord's citadel or the inner sanctum of the chaos cult. You've eliminated the guards. You are locked in battle with the masked overlord of all evil and in a brief pause in the fighting reach out and snatch away their mask. You gasp as you see ...
1-2. The Archduke or Archduchess
3-4. Your doppelganger (literally, a doppelganger in your form)
5-6. A faceless horror, or something with tentacles so the party can say, "Seriously, more Lovecraft?"
7-8. A goblin (he's standing on another goblin's shoulders)
9-10. Your old teacher
11-12. Your ex-lover or ex-mate or ex-best friend who always secretly resented you
13-14. Your mom!
15-16. The captain of the guard
17-18. The sergeant of the guard
19-20. Second man-at-arms from the left at the front gate who, now that you think of it, was giving you a funny look when you entered the city
21-22. The hunchbacked hedge wizard who hawks magic charms in the town square - turns out he's a 15th level magic-user
23-24. The high priest of the local Law Cult
25-26. The pirate lord of the western seas
27-28. The queen of the gypsies
29-30. A sleestak
31-32. A mannequin [gasp]
33-34. The mummified face of some the ancient pharaoh on display in the museum
35-36.
Nosferatu!
37-38. The princess royal
39-40. A ghoul [chomp]
41-42. Your evil twin brother or sister who was thought to have died in the barn fire
43-44. The head of the local merchant company
45-46. The local guildmaster of thieves
47-48. A bearded devil
49-50. A polymorphed fire giant, and that mask was what kept the spell in play
51-52. A brilliant light (choose a color) in place of a head that messes with your mind
53-54. A succubus - pucker up!
55-56. A tangle of vines and two emerald orbs for eyes
57-58. An elf lady knight from the far woodlands
59-60. A flesh golem with a psychic's disembodied brain sutured to its head
61-62. A serpent man with a cobra's ability to spit
63-64. The undying caveman
65-66. A grey alien with a headband of pain of dominance
67-68. A 15th level amazon
69-70. The wizened old magic-user you thought was your greatest ally
71-72. The dark pope of the holy assassins
73-74. A demi-god or goddess
75-76. A quasi-god or goddess
77-78. A primordial ooze thing that collapses into a blob of destruction
79-80. That dummy used by the seemingly harmless bard in the local tavern
81-82. A super-intelligent gorilla
83-84. A really stupid and confused gorilla
85-86. A heavily scarred visage
87-88. The twisted face of a maniac
89-90. A 15th level duelist who is actually left-handed
91-92. The emperor everyone thought was lost
93-94. The mad genius that designed the automaton palace guards
95-96. An astral deva that has taken Lawful Good to an unhealthy level
97-98. The Riddler (unfortunately, as played by John Astin, not Frank Gorshin)
99-100. The robe collapses, because the meme has been revealed