As of update 46.3, the Secret Elemenets menu was removed. It was previously displayed with the keybind RAlt + RCtrl. The elements from it still exist, however the only means to access the ones that only appeared in this menu currently is by console or duplicating them from older saves. This means clicking on them with the left mouse button while holding ALT to begin using them.

RIME

Rime is made when you freeze steam without giving it a chance to become water. It is a solid and electricity turns it to FOG.

FOG

Fog is made by sending an electric current through RIME. It is a gas and it moves like anti matter.

MORT

"Steam train." After being placed, it creates small low pressure wave sucking steam in what looks like a path/wall of steam. It is useful for smoke grenades.

LOVE

A strong, unknown solid element that forms instantly into the shape of a heart and is colored pink. It only appears in the secret menu.

LOLZ

Similar to LOVE, but takes the forum of the letters "lol" and is colored dark green.

FRZZ

It is believed that this element freezes anything that it touches. It is basically a very cold, extremely light liquid. It only appears in the secret menu.

FRZW

This element is a liquid form of FRZZ, essentially Water below 0 degrees but not ice. It only appears in the secret menu.

BIZG

BIZR in gas form, manually created by cooling BIZR.

BIZS

BIZR in solid form, manually created by heating BIZR.

BRAY

BRAY is created from SPRK'ed ARAY. The BRAY element rapidly fades after its creation with a life of 30 frames.

SPWN

Functions as a spawn point for Stickman [STKM] if he dies.

SPN2

Functions as a spawn point for Second Stickman [STK2] if he dies.

DYST

This element is dead yeast. Yeast dies when it is heated too much, or if Neutrons (NEUT) touch it. If dead yeast (DYST) is heated too much it will turn into Dust.

SHLD 1-4

Functions the same as SHLD, it is created when SHLD is Sparked.