DMB 1 said:
The feeling when the closest thing Ia had to a "Mon" game as a child was Invizimals.
Since nobody seems to recognize it, I'll briefly talk about it:
It was a series of games developed by the Spanish Company "Novarama" for the PSP and later the PS Vita (though one installment of the series was ported to the Nintendo DS), a PS3 game, and the last one is an app for Android/IOS.
The "main" series of games consists of 5 installments, which can be divided into the "PSP Trilogy" and the "PS Vita Bilogy"
The story of those games, (they are all direct sequels of one another), is basically about the characters discovering invisible creatures, called in fact "Invizimals" thanks to their PSP video camera (yes, I just said that), and learning to befriend them and to control them. As expected, the conflict is based around one of the characters wanting to use the Invizimals to conquer the world, thus becoming the main villain, which will last for pretty much the entire series, and later things will be pretty much balls to the walls because they get quite crazy.
The games, despite being basically Sony's response to Nintendo's "gotta catch 'em all" game for portable video game consoles, have more similarities with Digimon on that regard, like both Invizimals and Digimons being creatures from another world and with their own unique nature and physiology, them having something to do with technology, and with both being more story-focused, and the storyline themselves overall getting much darker than Pokémon's.
Because of the story taking itself pretty seriously, you can come across actually scary moments for a children's game, as well as unintentionally silly situations.
As I already briefly touched upon, the games' mechanics are based around the PSP's video camera and "virtual reality", the Invizimals themselves had to get captured all in their unique ways with unique gameplay, rather than just throwing a Pokéball at them and be done with it, which can make for some pretty fun, and unfortunately, tedious gameplay, especially because you can't just go around and do whatever the heck you want, but capturing every Invizimal in the section is REQUIRED to progress with the story.
On the other hand, the PSP Trilogy's battle system for Invizimal battles is... Weird. it's not necessarily bad, but it's a strange combination between a turn-based RPG and a fighting game. I have difficulty to briefly describe it with words, you'd have to see/play it yourself to understand it. The PS Vita Bilogy however, turned it more into a fighting game.
I'd go deeper with describing my experience, but I would basically never ned. I'll just conclude that the games, especially the PSP Trilogy, have e pretty underrated soundtrack. Just listen to a few of series' 2nd game's tracks:
https://www.youtube.com/watch?v=1RZVHNRfOEQ&list=PLygdVAAAqPOJtrMSSbPmhIOlwA4l89-jR