I will second the use of shrink item... I had a gnome illusionist who had a caltrop specially made at 16 times the size of a normal caltrop, or whatever that ratio was. Casting shrink item (or it may have just been called item in second edition) shrank it down to the size of a normal caltrop. I would have to recast it once a week or so to keep it in the appropriate size.
This gnome had a slingshot, and was usually a really good aim with it... At one point there was an enemy charging forward, roaring a battle cry. I loaded up my slingshot with my special caltrop, took aim, and rolled a 20. The caltrop landed right in the creature's mouth.
One command word later, the only problem the party had left was trying to get the gnome's prized caltrop clean.
I applaud your creativity but as a GM that maneuver opens up a lot of potential issues turning an item + minor spell into a vorpal, i.e. instantly lethal effect which if the GM turned around on you or did something equally creative, would potentially lead to an arms race and some serious friction at the table.
Back in AD&D 1e there was a guy who was very "creative" and he often voiced new uses for old spells, his favorite was destroy water which he believed could and should kill any living thing targeted because most living things such as people are 70% water. He even lobbied with other players to get an official house rule added to the campaign. Thankfully the DM put his foot down and said no.
Another "creative" player conned a DM into allowing this gem of a maneuver: he cast weighty chest on a slingstone bullet. This was a spell in the AD&D 2nd edition Tome of Magic. Anyways the purpose of the spell was to make valuable items difficult to steal. When someone not nominated by the caster (or the caster himself) touched the chest the spell effect caused the toucher to believe the chest weight 2-5 times the weight of the toucher so an average 200 lb person would believe the object weighed 400 lbs - 1000 lbs. There was a save but the player asserted that since this was an illusion and that the toucher had no reason to believe this was an illusion, there should be no save even tough the description of the spell read otherwise. Anywho the "creative" player then cast the spell on slingbullets which he slung at targets. Conveniently the player worked out the force = mass x acceleration effect of suddenly being struck by an object weighing 400-1000 lbs traveling at the speed of a sling bullet converted into AD&D terms. Simply put, it was far more effective than any other spell of that level. In fact it was a game killer after the player upped the ante by throwing handfuls of the stones at enemies.
Anothe creative type would carry dozens of quivers of arrows to turn over and drop on enemies from above because according to the rules the minimum damage from any successful hit was 1 point.
The list goes on an on. Simply put spells in some RPGs have fixed effects and shold not liberally be interpreted, in other games the effects are squishy and very open to interpretation and creative use. Players sometimes forget exploits work both ways but it almost always leads to unwanted conflict at the table.
For the record, I found your story entertaining as heck. Thanks for sharing. :D
I do understand where you are coming from here (I was the primary GM for my group all throughout middle and high school, and for a while afterward, and more recently with Pathfinder) but, and this is the important part, it was not an instantly lethal effect. I showcased the one time when it was, because it was entertaining. This spell is the same level as fireball, but usually did far less damage - I couldn't place the caltrop in the enemies mouth every single time (in fact, it only happened one other time, when fighting a dragon - it hurt the dragon a bit, but the creature was too large for it to do serious damage) and so it simply increased the damage to make his ranged attack a bit more potent.
The cases that you present seem to be abuses more than anything, and most of these can be countered quite easily. Ask the person who wanted to disintegrate water to show how his character found water in the body? Cut a person open and you don't see nice, clean water, you see blood. Blood is a vital force in magic, and thus is it's own separate element. Or state that the spell only works on something that is visibly water, obviously water, etc... It's good that the DM said no rather than caving in. There were a few times when some of my players tried something similar, and if what they wanted to do was suitably game breaking, I just explained to them that magic is not science, and what they wanted to do would not work the way they intended. They were a bit sad that their idea wouldn't work, but moved on to try something else.
As to the arrows, I think I would rule that the successful hit in this instance was the entire contents; he basically tried to upend the arrows on someone, and without the force behind it he may have been able to scratch the enemy a bit (hence one point of damage), it's just going to tick the enemy off. Basically he was trying to ruin the game on a technicality, and at that point the game stops being fun.
As a GM myself I try not to squash creativity - but if someone does try to bend the rules too far either it won't work, or (even more fun), it may not work in the way they intended. Or it may just not work as well as they would have liked. It varies from case to case, but being able to come up with ways to handle these kinds of issues on the fly has always been a strong suit.
Thanks for your reply, always fun to get feedback