Kou Dai Bao Shi: Yin (also known as Pokémon Silver) is an unlicensed port of Pokémon Ruby and Sapphire (originally released on Game Boy Advance) to the NES developed by SNT (short for Shenzhen Nanjing Technology). It's a rerelease of SNT's first game, only with a few minor differences such as the title.
Why It Sucks
Poor grasp of the source material: in the introduction, Professor Birch is replaced by Professor Elm, the Azurill is replaced by a Marill, and at the beginning, he is attacked by a Zigzagoon instead of a Poochyena (which only happens in Pokémon Emerald), which briefly turns into a Salamence as soon as the battle starts.
Many core mechanics of the Pokémon franchise are missing, most notably the inability to evolve your Pokémon, and instead you find evolved forms in tall grass. On that topic...
... In tall grass, you can find wild Pokémon that can't be found anywhere in the original games, such as Sunkern or Forrettress, and some Pokémon present in the originals are missing. Every Pokémon in battle also briefly turns into Salamence at the start.
The sprites for many Pokémon are also ripped from Pokémon Gold, Silver and Crystal.
The combat is broken beyond repair: due to technical limitations, there are only two moves in the entire game: one that deals relatively low damage, but has a 100% chance of causing your opponent to flinch, and another that deals higher damage, but doesn't have any side effects. The problem is that the player can't make the opponent flinch twice in a row, while the AI isn't subject to this limitation. This means that any opponent can deal high damage at best or outright cause your Pokèmon to faint while you are powerless to fight back.
The damage calculation system is very primitive: there are no types, stats or side effects, so the only parameter used when calculating damage is the level difference between the Pokémon in battle. This would've been a serious problem if the core of the combat wasn't already broken.
There are many glitches with the interface: for example, despite being able to choose only the male character, the player's back sprite belongs to the female character or wild Pokémon sprites not being loaded properly. Also, when buying items at a Poké Mart, you can't see the item you're buying, and in its place there is a picture of the Poké Mart seen from the outside.
Some warp tiles are glitched and don't work properly; the most notable example is the entrance to the Poké Mart in Oldale Town, which instead warps you to the first floor of the department store in Lilycove City, which you aren't supposed to visit until the second half of the game.
In every Poké Mart of the game, there is a door that brings you to a massive underground dungeon, complete with assets stolen from other games such as statues very similar to the Armos enemy in the first The Legend Of Zelda or floor tiles ripped from RPG Maker MV and downscaled to run on 8-bit systems.
There are only two soundtracks in the entire game, both of which consisting of 8-bit renditions of Oh! Susanna and get annoying very soon.
The game is actually a rerelease of SNT's first game, and there are only some very small differences. To add insult to injury, this release also introduces some bugs that weren't in the original release (such as the female back sprite used, regardless of the gender chosen).
Some maps are different from the original games, such as tall grass being present in Littleroot Town, where it's also possible to meet wild Pokémon.
For some reason, you can keep walking even when a character is talking, resulting in you being able to walk on text boxes.