FEATURES
Allows you to change the parameter names for certain classes (eg. hp, mp, tp, atk, def, agi, etc.)
Leave blank to use the default vocab names (specified in the rpgmaker database).
NOTES / ISSUES
Any script that uses the vocab will likely not recognise the class param names (and therefore use the default instead).
Combat messages and popups won’t use the class param names for buff/debuffs etc.
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Galv's RPG Maker Scripts & Plugins 
I get a error in the line 31 Syntaxerror ocurred
Tips for finding script errors:
https://galvs-scripts.com/errors-using-scripts/
Also try copying the script from the demo.
i do that and i get another error in the line 88 Type error
No implicit conversion from nil to intriger. (if i use the script alone or with scripts i get the same error)
My mistake, i see what cause the error of the line 88.
now i get the error of the line 88 but when start a battle (im using the yanfly battle engine and i set to true in your code)
This is an old script and really needs to be re-written. Unfortunately I don’t have time to do that the moment and the only thing I can suggest is this script needs to be under Yanfly’s
I’d like to note that, if using GTBS, this script needs to be beneath it, similar to Yanfly’s battle engine.
Here’s an odd thing. When I first installed the script, I added a third class section, and it worked fine. I ran some battle tests, and it worked. Then, five minutes later, having done nothing else to it, it suddenly won’t work. Said error on line 116 about implicit conversion, and there’s an if statement, but I’m not sure what’s wrong.
However, if I go back to the default code copied right from this page, the error is still on line 116. but now line 116 is just “def self.mp_a”
I thought it was because I had a skill that recovered MP, which is now called Ammo, but removing the skill does not stop the error. Maybe I’ll figure it out, maybe this just won’t be a script I use.
Never mind. Apparently, now it just works again, without any rhyme or reason.
It’s one of my first scripts and not a very good one – one day I’ll re-write it when I have time (if I ever get time again from being so busy… haha)