[RPG] What magic items grant you immunity to charm

Two things come to my mind immediately: Artifacts in the original AD&D DMG like the Rod of Seven Parts, and an extension of artifacts that I used in a D&D 3.5 game. Hopefully you'll get some ideas that will work for your game.

The AD&D artifact route is fairly straightforward: as you get more pieces of the artifact together, you get access to more and more powerful powers. So as you get more parts of the Rod, or collect more teeth, or gather the saint's remains you get access to more powers. If each part has a different basic power, it may make sense to have different party members "own" each item and pull them out to combine them as situations come up.

I don't think that's exactly what you're looking for, so I'll tell you about The Cubes.

In my game, the party stumbled onto a glass bracelet with a huge ruby in a treasure hoard. After some research, they discovered that its natural form is a glass cube with a smaller ruby cube inside it, hypercube-fashion. They discovered how to tune it to a specific person, and after some concentration and experimentation the wearer (he was a rogue, so it took him several levels of putting skill points in Concentration to do this) could get a direction on where the next piece lay.

Come to find out there are seven cubes, each dedicated to an ancient god. Each embodies an aspect of the appropriate god and provides a passive and active power to the wielder, but it must be in cube form in a hand to use the active power. So the Green Cube embodies Life and provides a continuous Death Ward aura, and it can be used to cast Heal once a day. The Red Cube embodies Fire so the wearer can heal when exposed to fire, and it can create a Meteor Swarm once a day. The Purple Cube embodies Magic so its wearer enjoys continual Arcane Sight, and it acts as a Rod of Spell Absorption up to 10 levels of spells.

Once the party started fitting the cubes together, they discovered that all the other cubes could adhere to the Purple Cube, and it would amplify or extend their powers using its stored spell levels. So a Purple/Green combo could increase the Death Ward aura into a Regeneration aura, or a Purple/Green/Red combo could call a green-tinged Flamestrike which would do double damage to undead but heal 1d8+5 HP to all living targets in the blast. The trick is, only the PC attuned to the cube can use it and control it. So multiple-cube effects requires several PCs concentrating to maintain contact with and control their particular cube.

Yes, we strayed from the rulebook a bit, but having the structure of World of Darkness Mage-esque keywords gave the players guidelines on what the cubes could do, and then their imagination took over. The life-powered Flamestrike was entirely my group's idea, but it fit within the realms of the cubes involved and the power level that the cubes could handle so it made sense to allow it. The purple cube can only absorb 10 spell levels, so a couple of 5th level effects would max out the effect unless the cube wielders wanted to tap into their active effects and "burn out" that power for 24 hours.

The spell levels of effects were pretty easy to figure in my head. There's usually a metamagic effect that's pretty close to what they wanted to make, or I thought of the effect as two spells cast at the same time. And yes, I granted bonus spell levels for really cool combo ideas.

These are really rough guidelines, and I never really codified the powers, but I took the basic inspiration from the Rod of Seven Parts, added effect keywords that I swiped from the Mage RPG, and fit the effects into the 3.5 system. I let my players flexibly define the combined powers, which got them really engaged in "I want to try this" playing as opposed to having them limited by their character sheets.

Your mileage will vary wildly, but hopefully you can get some ideas from my anecdotal ramblings.

First question: trigger

The character needs only to have at least one level of a class which can cast the spell. In this case a first level wizard will be able to trigger any wizard spell.

Second question: completion

From the SRD: Scrolls

To have any chance of activating a scroll spell, the scroll user must meet the following requirements.

• The spell must be of the correct type (arcane or divine). Arcane spellcasters (wizards, sorcerers, and bards) can only use scrolls containing arcane spells, and divine spellcasters (clerics, druids, paladins, and rangers) can only use scrolls containing divine spells. (The type of scroll a character creates is also determined by his class.)
• The user must have the spell on her class list.
• The user must have the requisite ability score. If the user meets all the requirements noted above, and her caster level is at least equal to the spell's caster level, she can automatically activate the spell without a check.

This means that the character must be a spell caster of the correct type (arcane or divine): so no a fighter will not be able to use a scroll.

If she meets all three requirements but her own caster level is lower than the scroll spell's caster level, then she has to make a caster level check (DC = scroll's caster level + 1) to cast the spell successfully.

In this case: yes a first level wizard will be able to try with any arcane scroll (if he has the required Int) but he will have to perform an appropriate caster level with the following consequences:

If she fails, she must make a DC 5 Wisdom check to avoid a mishap (see Scroll Mishaps). A natural roll of 1 always fails, whatever the modifiers. Activating a scroll is a standard action (or the spell's casting time, whichever is longer) and it provokes attacks of opportunity exactly as casting a spell does.

Use magic device

You can use this skill to read a spell or to activate a magic item. Use Magic Device lets you use a magic item as if you had the spell ability or class features of another class, as if you were a different race, or as if you were of a different alignment.

This allow to override the first condition: even if you are not of the correct class (or have the wrong alignment and so on) and you have the use magic device skill you can do a check and try anyway.

So in this case if your 20th level fighter is trained in use magic device: yes he can use a scroll