This is, by far, my favorite 2e spell. Even with all the limitations on it, it's the workhorse spell of any mage I've ever played. A lot of 2e players tend to look down on the spell however, so I'd like to discuss the spell and why it's absolutely essential for survival of a low level mage(and still useful at high levels).
The basis of this post is the Dragon Magazine Article "Survival of the Smartest" by Lloyd Brown III from issue 229. Though I agree with him on many points, there's one point I firmly disagree with him on. The savings throw. The cantrip as written has no save, and I believe it should remain this way. As the effects of the cantrip really aren't powerful enough to warrant one.
Take Bob the Wizard. Bob and his friends; Timmy the fighter, Jay the Thief, and George the Cleric all decide to go into a set of ruins. In one tunnel, the group of adventurers runs into a group of six goblins. The little monsters run screaming down the hall. Timmy and George stand in front while Jay guards the rear. Bob already cast cantrip about 15 minutes earlier(It has a duration of 1 hour per level, so casting it before combat even starts is a good idea).
Bob uses his spell to pull the pants of the lead goblin down around his knees during the creature's charge in an attempt to trip him. Cantrip offers no save, but the DM rules that the poor goblin gets a dex check to avoid tripping over his own breeches(50-50 shot). The goblin fails and goes down, slowing the other goblins down as they either stop to laugh at their companion's misfortune or try to move past him. George and Timmy take the opportunity to counter charge, with George bringing his mace down on the head of the prone lead goblin. Timmy sadly misses.
Jay then states that he wishes to try to Hide in shadows so he can attempt to sneak behind one of the goblins to take it down. Bob uses his cantrip to make the shadows twitch a bit, to help hide Jay's movements, giving the thief a +5% bonus to his Hide in Shadows roll. Timmy and George are hard pressed to defend themselves against the goblins, choosing to full defend to boost their ACs.
The third round starts and Bob asks the DM if goblins have any hair on their heads at all. The DM thinks a moment, and responds that the Goblins do have eyebrows. Bob grins and drops his concentration on the shadows, hoping Jay is in position, and targets one of the goblins, causing the creature's eyebrows to grow to almost a foot in length, drooping down over the creature's eyes, effectively blinding him. Timmy sees this and takes advantage of the weakened creature, dropping it with a single blow. George also attempts to make an attack but misses. Jay attempts to backstab one of the little monsters but also misses, revealing himself to be behind the group of goblins. The goblins manage to do no damage against the well armored George and Timmy.
The fourth round starts with two of the goblins breaking away from the warriors to take care of the thief. Both George and Timmy get to attack the two goblins, and one of the vermin goes down. Jay is evenly matched against his opponent. It would all come down to who manages to hit first. Sadly, Jay is a little too far away to get any aid directly from Bob, but the crafty wizard uses his cantrip to add a bit of weight to the goblin's sword, penalizing the creature's attack roll by 1. The goblin misses, and Jay hits taking the little monster down.
Now outnumbered 2-to-1 and partially surrounded the remaining goblins are looking nervous and are about to flee. Bob knows the DM is likely to roll for Morale on the creatures. Bob states that he's going to use his cantrip to make the shadows in the tunnel twist and move like they are trying to reach out to grab the terrified creatures. The DM believes that this use of the spell would merit a 1 point penalty to the Goblins' morale check. The goblins wet themselves and run screaming down the hall, but don't get very far as George, Timmy, and Jay cut them down.
This post is long enough, so I'll try to talk about non-combat uses a little later.