In the Chrome Extension version of the game (sometimes referred to as Spelunky HTML5), pressing both the search key and the reload key will max out your health, setting it to 99.
While the Spelunker may have a large amount of health, bear in mind that they are still not immortal, and are vulnerable to insta-kill methods such as Spike Traps or Crushing. The run can also meet its end through perma-stun, where the Spelunker is constantly knocked back and is essentially considered soft-locked.
If the Spelunker manages to get health by any other method while their health is maxed, the health counter will briefly display 100+ health before immediately correcting itself, once again displaying 99.
When pressing the search key and the reload key on the main menu, the screen will be flipped and mirrored, as well as open a new menu which is nonoperational. It can be closed using the escape key.
A drawing of a Cat in the Tutorial Level.
Underneath the exit door in the Tutorial Level, there is an engraving of a Cat in the wall. It is hidden behind the tiles, and must be uncovered with explosives.
In Levels with the Restless DeadFeeling, a grave with the name ASH can spawn. This grave will always contain a Shotgun, and is a reference to the protagonist of the Evil Dead franchise, Ash Williams.
Similarly to the cat in Spelunky Classic, there is another engraving hidden within the blocks of the tutorial level. This time, it is an engraving of the Classic Spelunker, and it is hidden directly above the Damsel, below the Shop.
Selecting the Pug Damsel 100 times will replace it with a Sloth Damsel, changing the skin for the menu as well as the whole run. The change is reverted upon exiting the game.
Sacrificing a Mystery Box rewards the Spelunker with an Eggplant, a mythical object of great power which is used in a long and arduous process involving the King of Hell.
Taking a photo of the Ghost with the Camera will cause her to pose in a humorous display.
The Restless Dead ASH grave easter egg makes a return in Spelunky HD, being nearly identical to the one seen in Classic.
There is a small chance, during any of the levels, for the musical theme to change to that reminiscent of the music in Spelunky Classic.
On the character select screen, there is a small chance for the bats to be replaced by an alien.
Similar to the HD version, taking a photo of The Ghost with a Camera will again cause her to pose, this time appearing close to how she was when she was alive.
There is a grave located near the top of Eggplant World. Using the Camera to take a photo of it will briefly cause a harmless version of The Ghost to appear.
Like the music reference listed above, there is a small chance that the Shop's Theme will change to that of one reminiscent of Spelunky HD's shops.
When pressing End Adventure, there is a small chance that The Spelunker will spill all of their remaining bombs on the floor in an active state, exploding seconds later.
