inferior version; worse version; knock-off
Used to describe something that is a clearly worse or degraded version of another thing, often with a critical or dismissive tone. Common in informal contexts, especially online.
This app is a knock-off of a famous game.
The new work is nothing more than an inferior version of the previous one.
模造品 is a more formal term for imitation or replica, without the inherent negative quality judgment of 劣化版.
Compound of 劣化 (deterioration, degradation) and 版 (version, edition). The word is a modern coinage, likely from internet slang, and is not found in traditional dictionaries.