These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Luigi seems uncharacteristically bold and confident in the Wii game. But then, not even he could be scared of anything in a simple board game, and he's sometimes portrayed as being good with money and gambling. (His intro quote for The Ghost Ship has him reacting as expected, showing that his cowardice hasn't been forgotten)
Game Breaker: Assuming you can get a long enough chain of shops, you can make shops with goods worth more than the average win condition!
That One Achievement: In the newest game there is a trophy obtained by buying every single shop on the board and winning. Naturally the AI will never let this happen, and successful attempts practically require a Free Play game that allows for three bankruptcies.
Values Dissonance: The series encourages insider trading as a viable strategy. In real life, insider trading is illegal in many countries (including Japan, where the series originated note Although the Japanese policy against it is comparatively lax).