For clarification, I restate my opinion that this is either pareidolia or a very interesting Pokemon premise. No offense meant.
Visually, if there is a lion, I wonder where its limbs are.
Anyway, perhaps this should be considered, if only for thoroughness. Or approached thematically.
Plus, a lion legendary after Gen 7 already did one? & why associate lions with optical illusions? Or Spain? Sure, Pokemon worlds aren't always like their real world equivalents, even with the Legendaries (No Hawaiian lions either.) but it helps to make sense for the region.
Plenty of animals, like zebras, tigers & a bunch of others use optical camouflage. Pretty sure spots & such are examples of this, too.
Although, I'm not sure which parts are the 2 glowing eyes. If there is a lion face in this image, it appears to be rotated slightly counterclockwise, as if the "lion" is tilting its head towards the viewer's right.
If this is an intentional optical illusion, or such, of a lion, I think "Pareidolion" would be an excellent name.
If it's the region's third Legendary, as a counterpart to Koraidon & Miraidon, then what about in relation to them? Lions & lizards/dragons? Perhaps it's a different species? A chameleon Legendary? A basilisk?
What about thematic relations? The best I can think of is that "time is an illusion". It is only which events are happening & their order; The system called "time" is just something humans invented to help us understand the world we're in. Supposedly, some animals experience time at different speeds than we do.
Relatedly, the "past" & "future" "don't exist".
In terms of physics & on a macroscopic scale, the universe is almost certainly never identical between 1 moment & the next. & no matter what, you are always living in the "present"; By definition, the past already happened, & the future hasn't happened yet.
Of course, I find the idea that the "past" & "future" "don't exist" kinda ridiculous, as we have proof past events happen, & many aspects of our future can be predicted & then witnessed happening accurately to our predictions.
Nonetheless, the point is that, in a nebulous manner, time, & more specifically related, the "past" & the "future" are illusions. But if their counterpart is the present, what illusion is there in the present? Optical illusions & pareidolia seem to fit that criteria.
....Although, the credibility of this theory is seriously hurt by that Miraidon & Koraidon seem to have less to do with the supposed illusory nature of time, & more to do with motorcycle dragons.
Should we expect such a layer to any hypothetical trio they might have?