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@DerVVulfman
Okay, here's the TEST Project. Not sure whether Gandalf is hiding in there still or not.

I downloaded your test file and tried it out. It indeed gave the error 236 upon playesting and opening up the game.exe file.
I tried changing around some things, and got nothing. I started fresh again and again.

THEN, I copy-pasted directly from DerVVulfman's post on here to the game, replacing what you had in the Runics script, and IT WORKED.

I wasn't sure what the difference was, so I decided to check, line by line, what may have been different.

I found no difference, which is starting to bother me.
Try copying and pasting directly from here again. Replace over what you had from beginning to end! If not, then I don't know what could be wrong.   
(Maybe Gandalf really is in your computer?!)

@Bounty Hunter Lani
Did that (lost count) several times and the error kept happening.
Which of DerVVulfman's Runic script did you copy that ACTUALLY WORKED?
I also kind of have to count on you, being a Bounty Hunter and all.
Hunt down this Gandalf imposter by copying that script which worked for you and show it to me. :P

If all goes well, I will let everyone know via post edit unless someone posted a reply after that. Not wanting to double post.

[attachment=965] 

This is what I have, let me know if it works.

@Bounty Hunter Lani
I think that way has better chances. Great idea there.
Can't test it right now so I'll make a post edit update soon.

Edit: It FINALLY worked. Runic Gandalf either gave up on blocking my path or ran away because of you. It's all thanks to you (not sure how you did it other than copy and pasting which worked for you but never for me the first time) and obviously @DerVVulfman who made the script(s) and @Kyonides who made some suggestions. Of course, to others as well who tried their best to assist me. With that all said, I can officially say THANK YOU ALL for your TIME, PATIENCE and EFFORT. It's unfortunate I cannot use my phone's Emojis. Oh well.

Edit 2: Now my only problem is setting up the Runic skill itself. I'm all ears for that one. There are some settings there I know like the SP cost is obviously "0" but I still have to make sure via "second opinion".

By definition the skill whose ID you've specified in the script will apply the status effect. Just be sure to set the scope to one ally (or all allies if it covers all of them).
Other than that, I'm assuming it doesn't have any healing factor so you don't need to worry about the HP settings or any of the stat modifiers.

Once the 'skill_effect' script in Game_Battler sees that the target attacked has the runic effect, it handles the effect of removing the damage and giving the target the spell's SP cost as a recovery factor.

When the runic spell is 'cast' on a subject to protect, it merely 'adds' the runic effect's counter and required animation data into the battler and then exits before anything ELSE is performed. So casting a runic effect spell on a subject prevents anything like healing, common events, status changes, etc.

So the only thing you need concentrate on within the spell database is the name, the icon, description..... SP cost of your chosen Runic effect (according to you, just zero).... the scope (ie single ally, all allies), ensuring it only works 'in battle', the animation effects with the 'target' effect being your barrier effect, and the variance setting which sets how many turns it can last before struck by a spell.

Still... I wanna look at your initial demo (above) just in case.

Grima Wormtongue has been whispering poison into your browser.

That is my guess.

Evidence #1: When you posted your code from the apparently affected scripts, the the Game_Battler and Scene_Battle code, I stated it appeared edited. This because the normal indent is a 2-character space indent, yet the first indent for every line of code you supplied was a mere 1-space indent.

Evidence #2: On downloading your package, I performed a detailed examination. All the default scripts are normal, including the standard 2-space indent all the way. And you are using the same .DLL file, so you and I use the exact same version of RPGMaker XP.

Evidence #3: Your demo delivered the odd error. But when I copied my Runic script in place of your pasted copy... it worked. More investigation with a refreshed copy had me investigate your copy of my script again. These are the points to make.

• Point 1: The actual syntax is correct, including the 'for enemy in...' lines.
  Retyping 'AFTER' the already existing indent still delivered the error.
  
• Point 2: Erasing the indent before the 'for enemy in...' lines eliminated the error.

In essence, illegal characters you could not see somehow made their way into your copy. As no one else suffered this, it could be related to the browser you're using... but that's a weird guess. But It is also odd that once I eliminated the illegal characters in the 'for enemy in...' statement, that illegal characters of the exact same nature appeared in the next FOR statement, 'for actor in .....'. And it continued for every other instance of 'for enemy...' and 'for actor...' which is itself odd... and very specific.

@DerVVulfman
Definitely my browser. I was using Microsoft Edge.
Maybe I should use Firefox or Google Chrome and see whether it works or not.

Will give a Post Edit update after because right now, I got a new error which I'll try to solve myself before I come back without Runic Gandalf.

Try eliminating the 'indented space' first