According to the AD&D rules somewhere in the Dungeon Master's Guide, creature's Hit Dice serve as the measure of their ability to overcome each other's magical defenses. I don't recall the numbers, but the meaning is that two liches should be able to cat-fight without worrying about each other's immunity to weapons under +1 enchantment, or that a dragon sufficiently old and powerful ought to be able to tear apart those same liches with its claws instead of flapping about like a big helpless fly. While this doesn't apply to high-level player characters, we have in the IE tools the functions to enable minions and enemies against each other or express a character's special supernatural power. I mean opcodes 344 and 345 - "Enchantment vs. creature type" and "Enchantment bonus." Rather than include them in weapons we can apply these effects to characters directly, permanently or for a time.
Can dragons hit someone protected from non-magical weapons in BG2? I don't know, but if they can, that's definitely because the designers equipped them with enchanted claws. If you make your own dragon, you can forget to add that property. And it's not feasible to specially reequip all powerful creatures, editing their claws and fangs so they can penetrate magical defenses. In many cases we don't even know what those weapons are called; and then someone will add a new creature and not include that effect. But we can patch the lot of them appropriately for their Hit Dice to strike through +1, +2 protections and so on. This way a sufficiently large spider you summon might actually be useful against a mage. Or a special blessing could empower a character against all mages for a time (opcode 344), up to their Mantle, with melee or ranged weapons.
Monks' fists don't use this opcode. Rather they are actual items replacing the character's hands... and they aren't enchanted, only have bonuses to hit and damage. But they should be enchanted, and there is no need for amputation with a direct 345 at level-up. My guy is not even a monk, but he just punched a flesh golem in the face.
This also goes for other abilities typically found on weapons or outside them. A permanent Free Action is an interesting possibility for a kit. Remove Gold on a melee hit doesn't have to be limited to Gold Digger, it is just as fine as a permanent property for a greedy by-the-numbers merc. And on the technical side, in this case the property was very easy for the designers to assign to the sword - it is not even a cast spell, just a Self-targeted effect lying calmly within the melee attack ability. When Melee hit is put on the whole person, as with a spell, it is tricky to target - it wants to cast the associated spell on the victim of the blow for any target type in the effect or in the EFF file. But it is possible to reflect it on the fighter if you include the Reflect opcode, 1 second long, against either the spell that the Melee hit is going to cast or the effect in that spell, in the hit-effects stack (and something against that glowing disc).
There is a handful of cases when people get to be enchanted this way, e.g. Quivering Palm, but mostly the games just create a weapon with those magical properties; well, there is a better way - enchant the person instead, and he will be able to deliver those effects as he likes. At least in some cases it is better. Chill Touch is pretty cool with that outlined hand, and with Ghoul Touch I suppose it makes sense that a ghoul really has to get his mitts on you, but Vampiric Touch? I see no reason why one could not drain life with a sword tip, especially since there are "vampiric" weapons proper. Vampires in AD&D can drain through weapons no problem. And the PHB version of the spell is not Instantaneous - the caster gets a turn to expend that power. But how to make sure that only one touch will be made over that time? The same way as before: include an effect removal on Original Caster with the damage and end the enchantment.
Let imagination bloom... We are in a desert...
