A mantacorn is a strange hybrid between a Manta Ray and a Unicorn. This animal only exists in strange LSD-induced dreams, and in the minds of young children!
Person A: Woah, trippy Person B: What do you see?
Person A: A mantacorn!
Person B: You're an idiot
Comes from russian word "Manyamirok" (Манямирок) which means Manya's little world. Manya (Маня) is a feminine russian name, on its own used online in reference to effeminate men, practice comes from a popular soviet film about prisoners Bespredel (Lawlessness), 1989. The phrase manyaworld is generally used on international social media platforms by russian speaking users when their opponent is speaking about political/social issues but actually has no clue how shitty the real world is.
A person mockingly quoting their opponent: >No! In my manyaworld repressing dissent is not needed to consolidatepower after the civil war.!