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.
DSTech has giant mostly invincible robots with guns that can shoot through concrete in-game. Concrete can't be shot through with a vanilla bazooka.
Due to the modding nature of the game, it's very possible for anything to be game breaking, via bug, design, or accident. One could even go into the files and improve all the stats on the vanilla game's weapons and make them able to destroy half of the scenery. As such, all references to game breakers found in mods, after the above ones, should only be very notable cases, including well done parody, a surprising use of, or one found in a quality mod large enough to be considered an expansion.
Using rockets as missiles. A rocket costs 50 gold, while a soldier equipped with a decent weapon will cost around 160 gold. One rocket can kill a whole group of enemies, inflicting massive economic damage. Put a bunch of cheap bombs in there and the rocket can be scuttled to guarantee instant death to everything within a 15 foot radius.
Good Bad Bugs: The vanilla thrusters on drones, robots, dummies, etc. gives a bigger boost than a sustained thrust. Thus, by spamming the jumpjet button and with some practice, an overly loaded robot can reach any point on the map.