What does Unusual Essence in Dota 2 do?

Question

I know its a bit late, but what does the Unusual Essence in Dota 2 do?

Unusual Essence 

A ball of swirling magical energy, pulsing with power.

I understand that the 3 basic Essences - Quas, Wex, Exort help shape the Weevil Egg, but I don't understand the use of a Unusual Essence.

Can anybody help with this?

Answer 1

The Unusual Essence can be applied to any Greevil Egg (up to three times), which gives the egg in the icon a glowing ring for each essence applied. Applying Unusual Essence(s) will give the courier that hatches from the egg unusual effects. Each essence applied results in varying levels of visual effects.

Note that you can apply unusual essences to any eggs on top of the max nine essences you can infuse in the Greevil Egg (so you can create a Seraphic Egg using 3 Quas/Wex/Exort and still infuse Unusual Essences into it).