story identification - Cartoon with a young unicorn and a demon

In the late 80s or early 90s I remember watching an animated series that followed a young unicorn and a demon.

In one episode the unicorn gave the demon his horn, and the unicorn almost died.

In another episode there was a man who was able to turn people into human shaped building blocks and built a huge tower from them.

Those are the two scenes I remember with any clarity.

Does anyone have any idea?

Answer

You're looking for the animated films featuring "Unico" :-)

Unico is a baby unicorn with white fur, a pink mane, and little cinnamon bun-shaped ears, who was born with the very special gift of making all living creatures lighthearted and happy. His friends include Beezle, the young Devil of Solitude; Chao ("Katy"), a naive little kitty who longs to be a human girl, and to learn magic from a real witch; a spunky little Sphinx, and a warm-hearted human girl named Cheri.

The Fantastic Adventures of Unico (1981)

This is the film where he loses or rather gives away his horn and gets into big trouble....

[Unico] agrees to hand over his horn to Beezle if he promises to be Best Friends Forever. With Unico's horn now part of him Beezle becomes even more 'spirited' (unbearable) and chases Unico around the island and eventually off a cliff, into the sea. Without his horn Unico is powerless and begins to drown...

Unico in the Island of Magic (1983)

This is the one with the castle made up of human building blocks....

Lord Kuruku plans to turn all living creatures, animals and people alike, into zombie-like beings called "Living Puppets" [these are the scary human building blocks in the movie] to be his slaves. Toby [Cheri's brother] works for Lord Kuruku, his job is to change people into Living Puppets and then lure them to Kuruku's island castle in exchange for learning more of Kuruku's magic.

^{~ Edited from Wikipedia and AnimeGames}