[Core bug] Slowdown in some levels of Mischief Makers

[Ryunam]

There is some clearly noticeable FPS decrease that happens in some specific levels of Mischief Makers (Yuke Yuke Troublemakers in Japan). Only the framerate slows down, while the audio and the music play without any interruption. I have experienced this anomaly with the Japanese version of the game at least in the following levels:

• Level 2-3. Very noticeable since the very beginning.
• World 2 Boss. After the initial cutscene, when you fight with the boss and block its punches, there is a noticeable FPS decrease.

This happens with the Parallel core when using either Parallel RDP or Angrylion, while it does not happen when using Mupen64Next-Plus with either the gliden64 or Angrylion plugins, so I'm assuming it is strictly a Mupen core issue.

Could also be related to https://github.com/libretro/parallel-n64/issues/616.

[Ryunam]

This is fixed with the Parallel-RDP implementation in the current Mupen64Plus-Next core, so it seems to be indeed a Mupen core bug.