That's just MILD and incubation, nothing really new. MILD is not about visual or mantra or anything like that, it's just about the creation of an association between the cue and your intention. Some people opt to visualize, some people focus on mantras, some people pratice intention, and seems you pratice into a specific cue (the horse). If it works for you, then keep trying, but don't trick yourself into thinking it's the content that turns you lucid, it's merely the connection. That way you'll know that the stronger that connection is, the more chances of getting lucid you will have.

The thing about reality checks is that they are more reliable than dream incubations. A 200ft horse may not appear in many of your dreams, but pre-existing dream signs do. Reality checks don't trigger lucidity by their own: they are responses to cues.