I have beaten the game with every known character so far and unlocked every krypt known so far and have not encountered any hidden characters or anything. Here are the few things left to explain that may help find more krypts or characters or whatever.
Village:
1Mystery key (supposedly unlocks the door behind where the boy first appears but I can't verify that and it should do more in my opinion)
2Ninja Star
3. Monk Temple that seems to serve no real purpose.
Earthrealm
1 Raiden Staff
2. people with the fish
Netherrealm
1. Netherrealm key (there is only one locked building in the netherrealm and it doesn't open that)
2. Kochal (gotta be more to it than 1000 onyx koins right)
Chaosrealm
1. The building that the monks are worshiping
Orderrealm
7 Walking on the clouds and A-9 (the -1 thing might have been a glitch but the A-9 thing seems deliberate)
Koffin WQ
The rest of the puzzle fighters
if you can answer any of these riddles besides what I have already pointed out let me know ( so don't tell me about Kochal being KOin ChALlange or the mystery key opening the hut I mentioned)
Village:
1Mystery key (supposedly unlocks the door behind where the boy first appears but I can't verify that and it should do more in my opinion)
2Ninja Star
3. Monk Temple that seems to serve no real purpose.
Earthrealm
1 Raiden Staff
2. people with the fish
Netherrealm
1. Netherrealm key (there is only one locked building in the netherrealm and it doesn't open that)
2. Kochal (gotta be more to it than 1000 onyx koins right)
Chaosrealm
1. The building that the monks are worshiping
Orderrealm
7 Walking on the clouds and A-9 (the -1 thing might have been a glitch but the A-9 thing seems deliberate)
Koffin WQ
The rest of the puzzle fighters
if you can answer any of these riddles besides what I have already pointed out let me know ( so don't tell me about Kochal being KOin ChALlange or the mystery key opening the hut I mentioned)