Release the chemical kraken!

Called the "Pharaoh's Serpent," this mixture of ammonium dichromate (NH4Cr2O7) and mercury (II) thiocyanate (HgSCN) creates a cool effect when heat is introduced. As IFLScience explains, as the NH4Cr2O7 burns, nitrogen gas, water, and ammonium (III) oxide are formed, and that creates the ashy, volcano-esque eruption.

The cool science, however, is just getting started.

The flame from the lighter also triggers a reaction with the HgSCN. As it heats up and expands, the mercury (II) thiocyanate turns into those dark, Cthulhu-like tentacles and becomes just carbon nitride.

This isn't something to do at home unless you have a safe chemistry set-up. Sulfur dioxide and mercury (II) sulfide are also produced in the chemical reaction, and you don't want to breathe in too much sulfur dioxide. (It's the same stuff that volcanoes produce, and it's toxic.)

This chemical reaction creates scary 'tentacles'
Bringing a flame to ammonium dichromate and mercury (II) thiocyanate results in the creation of a tentacle-like mass.