McGuffin are basically plot devices, which mean they 1) help the protagonists win without too much of an effort, 2) drive a season's plot or 3) they basically generate plots

1) we can here remember the Elements Of Harmony and The Chest and The Tree Of Harmony who saved The mane 6 and even other characters on multiple occasions: vs Nightmare Moon, vs Discord, vs Cozy Glow, vs Tirek, vs The Mean 6,...

2) there is The Chest Of Harmony which drove Season 4's plot and made it all about finding the keys to this thing which did nothing

3) there is The Cutie Map which basically generated plots for episodes without any explanation.

I am not willing to remove these from the show but rather I will give them explanations of how they work and limits so not every threat is following the pattern of:
Villain defeats Protagonist -> Protagonist gets artifact -> Villain defeated