In simple terms, this file is the for the SERP Pokérock Addon, specifically optimized for Minecraft PE/Bedrock version 1.21 .
Since Minecraft 1.21 introduced significant changes to the game’s engine, older versions of the Pokérock addon often crash. The "base121" version is the fix the community has been waiting for to keep their Pokédex progress alive. Key Features of the 1.21 Update file name serppokedrockaddonmcpebase121 top
If Pokémon look like black and purple cubes, your device might be running out of RAM. Try lowering your render distance. In simple terms, this file is the for