Once again, it seems a numbering error has crept into my spell roundup, but at least this time it's not (entirely) my fault, but that of the editors of the Moldvay Basic rules. I'll get to that a bit later. First, the tail end of the 2nd level magic-user spells...
9. Phantasmal Force: I'm given to understand that the rather incongruous name of this spell comes from its fantasy wargaming origins, when it was Phantasmal Forces (note the plural), which apparently was used to create illusory units of troops. Anyway...in B/X, Phantasmal Force allows the caster to create an illusion of anything desired, so long as it fits within a 20' cube, up to 240' away. It helps if the illusion is of something the caster has actually seen before. Can the 20' cube in which the illusion is contained be moved within the 240' range of the spell? The description doesn't say or strongly imply one way or the other, so DM's discretion. Based on the choice of words of the spell description (it creates or changes appearances) I would assume that the illusions created with Phantasmal Force are visual only - no auditory, olfactory, or tactile sensations are included. Illusions not used to attack disappear when touched.
Phantasmal force can be used as an attack spell, though any hit against AC9 dispels the illusion immediately, and all damage and other effects caused are strictly in the mind of the target. It's a lot more useful as a tool of concealment, diversion, distraction, or misdirection. An illusionary hazard - say, a pit or a wall - can dramatically alter the dynamics of a battlefield. An illusionary bridge over a real chasm could send a few enemies tumbling into the abyss. An illusion of something appealing can trick someone into touching something dangerous. An illusion of something mundane can make foes pass right by without a second glance. The possibilities are nearly limitless. For some excellent advice on illusions, see these posts at Hack & Slash.
The caster must concentrate to maintain the spell, so no putting up an illusionary wall and then walking away or going to sleep. Still, it's one of the most versatile spells a magic-user can know.
10. Web: Exactly what it says on the tin, this spell fills a 10' cubic area with tough, sticky, spiderweb-like strands. That's enough volume to block the average dungeon corridor, and most creatures will take 2-8 full turns to break through without burning the web. (Fire destroys it in 2 rounds, and creatures with giant strength can also break through in 2 rounds.) The primary use of the spell seems to be to trap opponents or to hinder their movement, but with a little creative thinking, it might have other uses. For example, cast it across a pit or chasm 10' wide or less, then toss a little debris on the sticky top surface, and walk right across. Or cast it as a safety net for a falling character. Sure, it'll take some time and effort to cut him out, but at least he didn't go splat on the hard cold stone.
The spell lasts a full 48 turns (that's 8 hours!) so you could use it to blockade the entrance to a dead-end room and get a full night's rest, so long as enemies with fire don't happen along. (And you could always suspend flasks of oil in the web's strands, so when the web burns, the flasks fall and break and ignite...)
11. Wizard Lock: It's sort of billed as a more powerful version of Hold Portal, in that it will work on anything with a lock, instead of just a door. The flip side of that criterion, of course, is that it has to have a lock, something which Hold Portal does not require. Wizard Lock also has the virtue of being permanent. The caster, or anyone using a Knock spell, can open the Wizard Lock without destroying it. Magic-using characters three or more levels greater than the caster can open the Wizard Lock without the use of Knock, though whether or not this ends the spell isn't stated. (I'd go with no, personally.)
It would make sense for every magic-user who knows Wizard Lock to use it on every door, chest, wardrobe, cabinet, and other locking container he owns. In the dungeon, it's not only good for securing doors behind you, but also for safeguarding surplus treasure from ordinary dungeon denizens until the party can come back for it, and for keeping cleared-out sections of dungeon relatively clear and secure from intrusions from unexplored areas.
Wizard Lock ought to have concluded the list of 2nd level magic-user spells, but wait a second...that's only eleven. These go to twelve! (Eat your hearts out, Spinal Tap.) The reason for that, and why it's only partly my fault, is that I was reading through the spell descriptions, not the numbered spell lists. It turns out, in the Moldvay Basic book, Detect Invisible appears at #3 on the spell lists, but there is no description given for it at all! Suspecting something amiss with my PDF copy, I dug up my battered old print edition, and it isn't there either. Huh. So, referring instead to the Mentzer edition rules, I give you...
Detect Invisible: This spell allows the caster to see invisible things at a range of 10' per level for 6 turns. That's pretty much it. I can see (or detect, if you will) why I never noticed the missing description in the Moldvay book. For one, except for range and duration, everything about this spell is completely intuitive. It lets you see things that are invisible. You could play an entire campaign, even an entire gaming career, without ever looking it up. Range? Well, how far can you see normally? Duration? One encounter sounds about right.
The other reason why I never needed to look this one up is because, using standard memorize, fire, and forget spellcasting, nobody ever picked Detect Invisible. Unless you have some reason to suspect that you're going to be facing opponents with the ability to become invisible, or your DM just has a penchant for using invisible enemies against you, there's no reason to take the spell at all. It doesn't do anything else, and there's not much room for creative off-label uses, either. It's potent within its niche, but it's such a narrow niche that memorizing it for an adventure is a huge gamble that's probably not going to yield any payoff.
You could make Detect Invisible more enticing by using Invisibility more often, both on enemies and on treasure and other dungeon features. Remember, it's effectively permanent until dispelled or the invisible creature attacks. If the invisible thing is an object with no attacks, well...
Tip off players that this may be the case, using the expedient of rumors (I hear the evil wizard left the Ultimate Spellbook in there somewhere before he ran off and became a lich, but he turned it invisible so nobody would ever find it!) Then make sure that some of those rumors are true, or that there's at least enough truth in them to make Detect Invisible pay off frequently enough to be worth it.