- In the second Lone Wolf book, Fire on the Water, you get the Sommerswerd. This solar blade carries over to later books and is the most powerful sword in the game. It can kill any undead enemy (including some otherwise unkillable). Some fans muse that this nerfed the game quite a bit, although in the second "season" bosses started getting stronger in the presence of the Sommerswerd, with powerups and weapons they wouldn't have had if you didn't have the item.
One of these actually has a boss which is mathematically impossible to beat if you happen to 1) have the Sommerswerd and 2) not have both rolled max attack value at character creation and 3) not have chosen the exact combination of Kai disciplines that give you the best combat side bonuses at this point in the story. Some gamers made up "Kai vault" house rules, purposefully opting not to take the Sword in that particular book (and invoked Fan Wank reasons to justify doing so, along the lines of "it's the only thing that stands between Sommerlund and the Dark Lords, Lone Wolf wouldn't risk having it taken from him during his dangerous travels"). Other, more dedicated players actually found a way to take the Swerd with them but have it confiscated by guards, then following a specific path that avoided all chapters where you got it back until after the boss, without any cheating.
- In The Fabled Lands series, it's rather easy to dial down the difficulty by starting in Book 6, then travelling back to the areas of Sokara and Golnir and cheesing several means of increasing all your stats as far as they will go up, until nothing at all can stop you. There's plenty of methods of Level Grinding by abusing infinite loops, allowing you to grind your money, stats and rank up to maximum with little to no effort.
Game Breaker / Gamebooks
Game Breakers in gamebooks.