You do get Riolu from an Egg. All the Gen 2 Babies are mandatory pre-evolutions meaning you can't get the basic forms in eggs. Gen 3 is when the very first "baby" (by your definition) Pokemon came out and that was Azuril. The only way to get an Azuril is to breed a Marill with Sea/Wave Incense. (can't remember which one). If you breed a Marill without the incense then you get a Marill. Fourth Gen expanded on this so Gen three was the first Generation to produce Baby Pokemon that can only be gotten from an egg and not through normal breeding.
List of Baby Pokemon:
https://bulbapedia.bulbagarden.net/wiki/Baby_Pokemon Both Togepi and Riolu are on the list.
For Jiranchi thing, Uhhh...Since the bonus disc was an official release of Jiranchi and was not an event. Therefore Jiranchi is not event only.
As for from the Spin off I said Manaphi wasn't event only. Also once again you bring in the Anime to a Videogame discussion. We've already been over that the Anime does things differently than the games. They are in two different universes and are two completely separate things. If all you can use to defend your point is pull out the Anime when it has nothing to do with the discussion or the details, then please don't even try to defend yourself.
I don't know how they classify Mirage Legendary Pokemon. I know Vicitini was called a Mirage Legendary on Serebii when it was released and they also classify Shaymin, Mew, Jiranchi, Celebi, and Manaphi as Mirage Legendaries. It either has something to do with why they are legendary or what ever reason they have. They get their information from another source, if you don't like the fact that are brought up go find the original source instead of trying to make up your own reasons to justify yourself.
And seriously learn to read I was clarifying the other person's post. Nintendo Event Only means that the Pokemon can only be recieved through an Nintendo hosted event like something from Wifi Central Mystery Gift function. Manaphy and Jiranchi can be gotten outside of Nintendo WFC and away from Nintendo sponsored Mystery Gift giveaways.
As for the Chibi factor, Yes Zorua has Chibi factor. It has a tiny body with a larger head. Something most of the babies have going on. Does it pass to normal Pokemon, I think so, but majority of the Chibi Pokemon are babies. Most look like chibi versions of their Basic forms. Only exceptions to that are some of the Gen 4 baby Pokemon and Tyrogue since it evolves into three Pokemon and Togepi.
Now I saw you mention Action Replay, Well seeing as we are talking about official ways to catch/Own pokemon and you bring in cheating I'm pretty positive you don't know what they hell you are talking about. The Action Replay can get you anything and is a very poor attempt to defend your point.