Three years ago I figured that it would be good to come up with a way to randomize this for Swords and Wizardry.
I coded up the tables using NBos' Inspiration Pad Pro and tweaked the results until they look about right. After that I had everything I need to write up Random Memorized Spell Generation for the Majestic Fantasy RPG. Note that the I used the spell lists out of Swords and Wizardry Core edition.
In the 2017 post I talked mostly about the difference between random tables and random assortments. However I didn't get into how I weighted the tables.
It been my experienced that with all else being equal some spells are just more useful than others. That they are useful in more situation than other spells. So rather than assigning an equal chance to all the spells being memorized, I weighted the result based on my experience roleplaying and refereeing magic users.
For example 2nd level spells for Magic Users
Common Level 2
1 Darkness, 15' Radius
2-3 Detect Evil
4 Detect Invisibility
5-6 Detect Thoughts
10 Locate Object
11-12 Mirror Image
13 Phantasmal Force
19 Wizard Lock
20 Uncommon Level 2
Uncommon Level 2
1-15 Continual Light
Adjudicating the usefulness of spells
The first thing about the 2nd level spell list for magic users is that there is no single goto spells. For first level Charm Person, Magic Missile, and Sleep are very common. For 3rd level you have the ver popular Fireball or Lightning Bolt.
For 2nd level spells the most common I have taken as a magic user for my 2nd level spell slot is web. It effectively immobilize your enemy within in its area of effect and also serves as a barrier. However Detect Evil, Detect Thoughts, Mirror Images also all seen frequent use. The least commonly used spells in my experience are Continual Light and Pyrotechnic. The rest of the spells all have their uses in various situation.
So I am going to weight the odds of memorizing second spells like this.
Detect Evil, Detect Thought, Mirror Image
Darkness, Detect Invisibility, Invisibility, Knock, Levitate, Phantasmal Force, Strength, and Wizard Lock
Continual Light and Pyrotechnics.
The tough call is Invisibility, arguably it probably a 2 1/2 Tier spell. I wanted to use a d20 roll as the randomizer and keep the sub tables to a minimum. So I decided that Mirror Image had enough of an edge over Invisibility to warrant a 10% change as opposed to a 5% chance. The main reason is that Invisibility drops if you attack and Mirror Image lasts for the duration of the spell and potentially prevent crippling damage.
Feel free to rework the tables if your judgement call on various spells differ from mine.
Another spell I will be re-evaluating is Phantasmal Force. I don't have the link but on one of the old school forums somebody did an analysis of the history of the spell.
If you look in Chainmail 2nd edition, the one that predates the release of Dungeons and Dragons on page 28 to 29 you have.
Phantasmal Force (Chainmail 2nd Edition)The creation of the apparition of a unit or creature for four turns, maxi-duration.
In Original Dungeons and Dragons you have
Phantasmal Forces (ODnD)The creation of vivid illusions of nearly anything the user envisions (a projected mental image so to speak). As long as the caster concentrates on the spell, the illusion will continue unless touched by some living creature, so there is no limit on duration, per se. Damage caused to viewers of a Phantasmal Force will be real if the illusion is believed to be real. Range: 24”.
Here it is a more general purpose illusion spells but still echoes it use in Chainmail. Swords and Wizardry adapts the above but added an limitation that the illusion can only be used to deal up to 2d6 damage.
So I decided to alter the spell in the Majestic Fantasy RPG to the following. To keep it utility as an illusion spells but also to call back to its original use in Chainmail.
(Magic-User, 2nd Level)
Range: 240 feet;
Duration: Until concentration ends;
MI: Yes; Art: Web;
The caster creates a realistic looking illusion of a creature, object, or effect. When the illusion is touched or attacked, the character makes a saving throw. If the save is made, the character realize it is an illusion and the illusion is dispelled. If the save is failed, the character believes the illusion is real.
Phantasmal Force can also be used to create a creature or effect that is capable of inflicting damage. Anything that is capable of dealing 12 points of damage or less can be created as an illusion with this spell. For example a wolf or a flaming pool of oil (does 1d6 per round).
When a target is attacked they get a saving throw vs spells to see if the target know it is an illusion. Success means the illusion is dispelled, failure means the target believes the illusion to be real. Combat is then resolved using the normal stats of the creature.
Focused Art: The illusion is more effective. Creatures or characters that can deal up to 18 points damage can now be created by this spell.
The changes make Phantasmal Force more like a Summon Monster spells except those interacting with or are attacked by the spell get a saving throw.
I think this removes a lot of the grey area for how Phantasmal Force is used in combat and increases the utility of the spells compared to its original wording.