I'll do my best :)

Nintendo is suing palworld for patent infringement, meaning it thinks palworld is infringing (using without permission) one of Nintendo's patents.

These parents went through the application process and the Japanese patent office decided they were valid (basically that they were new and inventive).

Now, though, the validity of 2 of the 3 Nintendo parents are having their validity questioned.

A pending Nintendo application (not yet a patent) is, at the moment, considered to not be patentable because it lacks the new and inventive part that is required of a patent. This was discovered because a third party told the patent office about something that existed in some sort of publication before the Nintendo application was started (basically). This earlier-existing thing is called prior art. Prior art is sort of like a quasi-patent in the sense that new applications' new and inventive determination is based on basically all previously existing stuff. Just because Nintendo didn't disclose it and just because the patent office itself didn't discover this prior art doesn't mean it does not still operate to block the new application's new and inventive idea.

Now Nintendo has to demonstrate to the patent office that its new application is actually different from the prior art or that the prior art should, for some reason, not actually qualify as prior art. If it is successful, it can become an actual patent (assuming all the other stuff it needs is correct).

This all matters because this new application stems from existing Nintendo patents. This means basically that Nintendo patented something extensive that can be broken into smaller parts that are also patentable. This is confusing but it's sort of like if you designed a 3-in-1 hot coffee, espresso, cold brew machine (on paper). It was so unique that if you separated the espresso part of it it was still new and inventive over everything else in existence, which makes it patentable. As well, if you separated the cold brew part, it was also new and inventive (therefore patentable).

This new application is like the cold brew part of the example above. The espresso part was already found to be new and inventive (now a patent) but the discovery of this third-party prior art is not only blocking the new and inventiveness of the cold brew part (new application), but also of the entire 3-in-1 machine (already a patent). This could happen, for example, if someone in India invented the 3-in-1 machine but the Japanese patent office didn't know about it and Nintendo didn't know about it when Nintendo first tried to patent its 3-in-1 machine with the Japanese office. Now, the India machine has been brought to japan's attention during this new application and it could lead to the office reconsidering the validity of Nintendo's 3-in-1 machine altogether.

Hope this helps! I tried to make it easy enough to follow with a more imaginable example but the whole thing is still pretty abstract and confusing.

As I understand Pokemon GO and other games had monster capture mechanic before patent submission and patent is invalid in non-final verdict.