There are several
things spread across the Final Fantasy series that nobody would’ve ever
discovered legitimately without a guide. From recruiting Gogo in VI, which
required allowing one particular monster to swallow all four party members in
battle, through to acquiring the Excalibur II sword in IX, which required the
whole game to be beaten in a near-impossible 12 hours.
Obtaining Doomtrain in Final Fantasy VIII is up there with the worst of these, requiring the player to collect six of three different items, one of which is only obtainable through an otherwise useless refinement ability from a missable summon, and then use another item, hidden in an optional location not visited during the story. There is no hint to this process apart from subtle nods in four in-game magazines, all but one of which require the player to stray far from the beaten path at one specific time or they can never be read.
Those that actually succeed in this quest are rewarded with a fantastic summon. Doomtrain’s appearance is terrifying and summoning it inflicts a myriad of horrible status effects, including the reduction of defence to zero, on all enemies. Throw in the ability to craft god-tier items like Elixirs and Megalixirs and it becomes an essential endgame companion, albeit one that has never recurred since.