Cuphead

ALL Hidden Coin Locations:
If you search the following locations you will find ALL 7 hidden coins.

World 1: Inkwell Isle 1

Coin 1:
When you complete the tutorial you will get the first coin.

Coin 2:
Defeat ALL the bosses in Inkwell Isle 1. The Axeboy will then move aside and the second coin can be found in the trees.

World 2: Inkwell Isle 2

Coin 3:
Go to the Aviary Action Boss stage and then go behind it. If you now move to your right you will locate a shortcut to the other side of the island. If you take the shortcut you will reach the Gingerbread Girl in front of Aviary Action and get the third coin.

Coin 4:
Near the Dragon's level you will meet a juggler. Complete his challenge (parry four times before landing), then return to him to get the fourth coin.

Coin 5.
Near the exit to Inkwell Isle 3 you will find a green shack with the fifth coin in front of it.

World 3: Inkwell Isle 3

Coin 6.
If you look behind the stand near the theatre you will find the sixth coin.

Finale

Coin 7:
If you look behind the stairs outside the casino you will find the final coin to the left of the stairs.

Unlock Alternate Endings:
Complete the following tasks when you fight The Devil at the end of the game to unlock the corresponding ending:

Bad Cuphead Ending:
Begin fighting The Devil and agree to give him the Soul Contracts when asked during the opening cutscene. In this ending, both Cuphead and Mughead are seen having gone insane and are rotting in hell with The Devil.

Good Cuphead Ending:
Begin fighting The Devil, but choose not to give him the Soul Contracts when asked during the opening cutscene. If you then defeat The Devil you will be able to view the 'Good Cuphead' ending where you run home and tell everyone they are now safe.

Unlock Expert Mode:
When you complete the game the Expert difficulty setting will become unlocked.

Unlock Black and White Filter and Vintage Mode:
If you talk to the turtle that is sitting on the dock in Inkwell Isle 3 you will get a hint about seeing the game in gray. This hint is referring to completing the platforming levels without shooting any enemies. Listed below are the six platforming levels:

Forest Follies
Treetop Trouble
Funfair Fever
Funhouse Fazzle
Perilous Piers
Rugged Ridge

Although you cannot use your gun you can use supers that grant invincibility, dashing, and parrying. When you complete this task on all six platforming levels with a 'P' grade and then talk to the turtle again you will unlock the 'Black & White' filter which changes the display to black and white so it has a 1930s retro style appearance while Vintage mode alters the audio.

Unlock 2-Strip Mode:
If you talk to the fork standing outside the shop in Inkwell Isle 3 you will get a hint about getting A's in the game. If you do manage to get mostly 'A' grades for all the Boss fights on the 'Checklist' and then talk to the fork again you will unlock the '2-Strip' filter, which changes the display to a two strip limited colour palette. Note: Getting a few 'B' grades will still unlock 2-Strip mode.