"Αυτό είναι το άλογο μου."

Translation: This is my horse.

[xobox3]

There should be another accent on the second omicron: το άλογό μου
because μου is clitic and άλογο is stressed on the third last syllable.

[Djenthallman]

Then how does one say: "This horse is mine"?

"Αυτό το άλογο είναι δικό μου"?

[D_..]

Correct!

[CatNephE]

This one always reminds me of : https://youtu.be/wSYpsRJuWdA !
It's one of my favorite scenes in Ed, Edd, and Eddy and Rolf is my favorite character. I think my love for Rolf is part of why I love the funkiness of the Greek language and Greek music. <3

[Nefritees]

Could, "that horse is mine" work?

[jaye16]

Yes, that is also correct.