MrTS_MonsterBook causes the savefile size to increase over time with no limit

[Mac15001900]

Adding new items to the list of revealed items does not check if those items are already there. As a result, the amount of data in the savefile grows every time any monster is killed, with no bound. This can cause savefiles to reach very large sizes (e.g. 7MB, while going down to 120KB after clearing this plugin's data).

See this discussion on the RPG Maker Forum for more discussion on the issue, and the fix to it.