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.
Motaro appears out of the blue in a random Earthrealm village in the Konquest mode to give you some koins, then vanishes. It's a rare occurrence and the player has to be quick to make it happen, so it's more of an Easter Egg.
Meat randomly appears with a British accent in the Netherrealm in the Konquest mode to give you some koins, then disappears.
Crazy Awesome: Havik. How many fighters do you know crack their own necks to regain health, and slide across the floor like a penguin?
Designated Hero: Shujinko, mostly because he can't see through Onaga being a bigger dick, but you're still encouraged to rob everyone blind for the hell of it if you want to unlock everything, and a lot of problems are "solved" by just sucker-punching random people.
Game Breaker: A ton. The majority can be corralled under two things: moves that lead to unduckable throws, and moves that can be repeated ad-nauseum until the timer runs out. It's the core reason why this game was frowned upon by the professional fighting game community.
Dairou's Tombstone Drop is this. It's an unblockable ground pound that falls extremely fast and has a very quick recovery time, and the only way to avoid it is to anticipate it coming and jump. Unfortunately, given this game's mechanics, that's a lot easier said than done.