amok: Before all the armchair lawyers start sprouting the usual rubbish:
1) This case is filed in Tokyo, Japan. Both Nintendo and Pocketpair are companies legally operating from Tokyo, which means this case falls 100% under Japanese jurisdiction. Japanese trademark, patent, and copyright laws differ from those in the USA, Europe, or international law (where armchair lawyers almost alwways use - "But my fair use!!", no, this only applies to the USA). Japan has stricter patent and copyright laws. Unless you are well-versed in Japanese law, any claims you make will likely be unfounded guesswork. To understand the relevant laws, you should at least have knowledge of the Japanese Design Act, a translated overview here -
https://www.japaneselawtranslation.go.jp/en/laws/view/3269. Though other laws may apply as well.
2) This is neither a copyright nor a trademark suit; it is a breach of patents case. Without knowing exactly which patents are being sued over, everything is speculative. Patents are very specific. In this case, I will assume they involve some design patents, but that is merely a guess on my part; it could be something else. Nintendo may have found some copied code, who knows? Until more detailed informaation - not me, and not you.
3) You cannot (not even in Japan) patent a game mechanic (e.g., a mechanic based on catching monsters). You can patent specifics around it, e.g. the code used to implement that mechanic (though any different code achieving the same result would be fine), or the design you use to depict the mechanic in action (e.g., a red and white pokeball).
