Today’s challenge? A no-brainer for me. Without hesitation, I choose one of the most powerful monsters in 1E’s Monster Manual. Yes, that’s right. I choose the leprechaun.
Sure, a leprechaun only has 2-5 hit points. Sure, he has zero attacks that inflict nil damage. Formidable limitations for a most powerful monster, but it’s what the leprechaun can do that makes him dangerous. First off, he’s 80% magic resistant. That means he’s 100% magic resistant for magic-users 7th level and below. You can’t surprise a leprechaun; his keen ears prevent it. The leprechaun also “can become invisible at will, polymorph nonliving objects, create illusions, and use ventriloquism spells as often as they like.”
Notice that the second and third abilities on that list of magical powers don’t have exact spell equivalents. The list doesn’t say a leprechaun can use polymorph other or phantasmal force. When I used leprechauns in my 1E games, I interpreted polymorph nonliving objects to mean that a leprechaun can use polymorph any object as long as the object being polymorphed starts out as nonliving. Create illusions meant that, if it’s an Illusion/Phantasm spell, a leprechaun can bring that effect into being.
So, yes, a leprechaun could bring that bronze statue to life as a giant. A leprechaun could turn your PC’s rope into a python, or his sword into a sunflower. A leprechaun could set up a Leomund’s trap to befuddle thieves, get an adventuring party lost in a hallucinatory terrain, or trick a foe with spectral force. And he could do most to all of this while invisible.
I remember gamers with belligerent styles of play becoming obsequious when the leprechauns came out to play. The consequences for escalating the encounter with violence were just too great to risk.