As others have pointed out in version 0.0.1 it is quite impossible to lose to truck-kun within reason. (possibly actually impossible depending on how the attack patern is coded) after several attempts i did not manage to get below 8 hp while only doing standard attack. After that I did block only for about 300 turns as to not kill it and it only attacked me 4 times in total an d only once on a block. In the end I did manage to lose by editing my save file to me only having 1 hp remaining before the fight starts. For now its not worth the effort to explore what happens after you lose. It leads to a monologue by the developer into a game over screen.