I'm not quite ready yet to write a post on re-redesigned devils or other infernals, so I've been reading through the Nethack wiki instead. That's sort of the inspiration behind the mana post. But also it's been inspiring ideas for a more-detailed player tricks. There are all sorts of tricks in Nethack for identifying different items: dipping violet gems in potions, engraving on the floor with gems or wands, dropping rings in sinks. There are other tricks that provide various benefits, like dipping items in holy water or dipping a long sword in a fountain. For D&D and tabletop RPGs in general, it's better to improvise such effects, especially those based on the known properties of real-world objects; but it would be useful (and fun!) to have some guidelines for "fantastic tricks" similar to those in Nethack.
One trick in Nethack is to engrave Elbereth on the floor to provide protection from monsters. You wouldn't want an obvious, universally-useful, permanent form of protection in tabletop play, but here are some ideas for an Elbereth-like effect: etching a name of power into a surface will provide limited protection against intelligent or supernatural monsters. Treat as a Turn Undead command from a 1st level cleric, comparing the hit dice of the creature to those of undead creatures. The effect is short (up to one hour,) and does not prevent the use of normal thrown weapons or missiles.
The trick is that there are three names of power, and no one will know what these are at the beginning of the game. Randomly generate three names for games using the three-alignment system; each name will "turn" creatures of one alignment. The names must be discovered through clues or research, and the alignment links must be discovered through trial and error.
If desired, there can be additional, harder to discover names that have higher-level effects; a 7th level name of power, however, should probably include a risk of something unpleasant happening as well.