When a leprechaun teleports after taking gold so they can bury it, if there is a leprechaun hall on the level, they will always pick a random unoccupied space in that room to teleport to. (If no space is unoccupied, they will teleport randomly as normal.)
Leprechauns should sometimes wake up when someone is moving near them carrying a large sum of gold. Their awareness doesn’t extend to the precise location of the creature, it’s just enough to shake them awake.
The chance of this happening and/or the distance at which this happens should be dependent on the amount of gold carried.
Leprechauns very rarely drop a four-leaf clover on death. This is a vegan comestible that provides 1d3 luck (or just acts as a luckstone) when carried and can be eaten to gain 1 Luck. (The four-leaf clover appearing from sacrifices is not this item and cannot be picked up, though that could become confusing.)
If a gold golem is hit by a gold-stealing attack, some gold pieces are put into the attacker’s inventory and the golem loses some of its maximum HP.
Leprechauns have a tiny chance, less than 1%, of dropping a credit card on death (or generating with one). Such a card will always be a “Yendorian Express - Gold Card” or “Shamrock Card” when read. They also are capable of stealing any credit card that says either of these things.
Leprechauns have a one-way grudge against gold golems and gold dragons.
Cut down on the list of inediate monsters by defining some of them to be either herbivorous or carnivorous (note that the game uses carnivorous to mean “can eat meat” rather than “only eats meat”).
Herbivores:
Carnivores:
Vault guards grudge leprechauns.
Give a YAFM when near or chatting to a hallucinogen-distorted leprechaun: “They’re after me lucky charms!”
Leprechauns do massive damage to gold golems.
Leprechauns steal credit cards as well as money.
Leprechauns steal potions of booze as well as gold.
Leprechauns are occasionally generated with a sack of gold rather than gold pieces in free inventory. Though this would either have to be quite rare or only be possible on leprechauns generated outside leprechaun halls.
Leprechauns (or anything with AD_SGLD) should steal items made of gold out of the hero’s inventory.
Carrying gold items openly causes leprechauns, dragons, and Croesus to be automatically aggravated.
Leprechauns steal anything made of gold, in addition to plain gold pieces. (In vanilla, the only gold item is the gold ring, but variants have other gold items.)
