Various proposals for things to happen on St. Patrick’s Day:

• Leprechauns should get buffed. There are various ways this could be done; probably the easiest is giving them more starting gold but also increasing the damage of their attacks.
• Leprechauns could spawn with potions of booze (always for individual leprechauns, low percentage chance in leprechaun halls). Ideally, the potion should be green.
• When random gold piles generate, leprechauns should frequently spawn on them.
• Random gems should have an elevated frequency of emeralds and green worthless glass.
• If the game is started on St. Patrick’s Day, the potion of booze is always shuffled such that it’s green.