Agreeing to Bad Ideas

[Greenfield]

The whole situation seems like something to avoid.

I strongly recommend a liberal use of the word "No".

<Tangent>
I had a player who wanted to join my game. He wanted to run a Half Balor.

I, conversationally, asked if the character was built with the Half-Fiend or Fiendish templates, and what his class levels were (We were running around 14th level at the time so this wasn't as insane as it sounds.)

No, he wasn't made with anything like that. He didn't have any class levels or specific abilities, he was just what the player thought a Half-Balor should have.

I expressed extreme doubt, saying that the concept was intriguing (even though it was a very bad fit for the team), but that he'd have to create it by the rules. You know, class levels, templates, ability scores that could be accounted for, specific skills and skill ranks, feats. You know, follow the rules.

Figuring that I'd see the Mark II version soon enough, I let him in. He tried to lever the character into the group, not with a coincidental meeting or even a shoe-horn. No he used a crow bar. A full Balor appeared, challenged the party, and when we failed to run like hell he figured we were the people who could take care of his son. But if we didn't do a good job he'd be back to punish us.

I pointed out that it was the DM's job to introduce characters, and that players weren't supposed to take over the narrative, not introduce foes and/or make threats. The player didn't understand the objection. He was apparently used to bullying his DMs and getting pretty much whatever he wanted.

Long story short, he didn't see why he should change his character from the featureless blob of power (pretty much any power he thought was needed for the situation), and so was not welcomed back for a second session.
</Tangent>

My drop-in seems like a more extreme version of your player. Rules are for lesser mortals, he wants to invent his own.

I suggest a casting of Empowered, Maximized, Twinned Dispel BS.

 

[Schmoe]

You'll laugh, there are two very similar things in AD&D2.
1. Sha'ir from Al-Qadim has unlimited spell procurement. His gen familiar can fetch any spell Sha'ir have seen cast personally or existence of which is "common knowledge", unlimited times/day, but only one at a time and with at least 10% failure chance, depending on his level, spell level, and some other things. Base time is 1d6+spell level rounds (if he could cast this spell as a normal wizard), turns (if couldn't) or hours (if it's foreign or priestly magic), and there are possible problems if he goes for divine spells. Or his gen familiar may simply get lost for a while. Speaking of whom, he'd better treat his gen well.
2. Nahal's Reckless Dweomer. It's wild magic, of course. Allows to shape any spell the wizard personally knows. It automatically generates a wild surge - if the result mentions the cast spell (such as "spell works, AoE is doubled, if any", or "spell is deflected to the random target in range"), it goes off, otherwise he just caused a wild surge, and that's it.

There are 3.x conversions for both - Wild Mage in Complete Arcane, Sha'ir in Dragon #315 (and Dragon Compendium).

Both of those are great models to use as baselines for what the player proposed. Each one imposes a significant drawback that prevents abuse. In the Sha'ir's case, the time waiting for the gen to return is a huge limiting factor, as the Sha'ir can only really have one spell at a time and has to wait at least 2-7 rounds between each spell. In the wild magic case, the very real risk of a wild surge is the limiting factor (less than 50% of casts involve the actual spell).

As presented, the character's request is well beyond the power curve of what I'd allow in my game, but with the right balancing restrictions it could certainly work. I have a hunch, though, that if you impose those restrictions your player won't be interested.

 

[TBeholder]

The whole situation seems like something to avoid.
I strongly recommend a liberal use of the word "No".

This is always (well, almost) an option, but there's a great distance between making marysues to forcibly insert them everywhere and trying something. The cases closer to the second often have a legitimate niche.

I pointed out that it was the DM's job to introduce characters, and that players weren't supposed to take over the narrative, not introduce foes and/or make threats. The player didn't understand the objection. He was apparently used to bullying his DMs and getting pretty much whatever he wanted.
Long story short, he didn't see why he should change his character from the featureless blob of power (pretty much any power he thought was needed for the situation), and so was not welcomed back for a second session.

Hmm. I suspect that was not a Munchkin, but a more terrifying creature. You have encountered the dreaded Fanficgame player! They nest mostly in LiveJournal, but sometimes leave their habitats to sow abject horror among the unprepared dice-rolling folk.
Then again, Fanficgame GM seems to be worse, but even they are not always hopeless.

Both of those are great models to use as baselines for what the player proposed. Each one imposes a significant drawback that prevents abuse.

IMHO Sha'ir also requires some roleplaying ability to do properly, since it has inherent RP component comparable to divine casters.

As presented, the character's request is well beyond the power curve of what I'd allow in my game, but with the right balancing restrictions it could certainly work. I have a hunch, though, that if you impose those restrictions your player won't be interested.

Probably, but who knows. There are all sorts. May be munchkin, may be newbie, may be a proper roleplayer with experience limited to very different games. I certainly remember there was some "okay, this effect is 3 dots in this and 1 dot in that" magic system, but can't remember which (didn't play it myself).