As for why Darkrai had made Snorlax angry, it was actually rather funny.
Because Darkrai had once competed with Snorlax in an eating contest, Snorlax would often drag Darkrai along whenever he ate afterward.
(Hoopa Valley, where Snorlax and Darkrai competed in an eating contest.)
But Snorlax was no longer as weak as he used to be. By chance, he discovered that Darkrai had not actually eaten all that food, but had secretly stored it in his own pocket dimension.
The moment Snorlax saw that, he exploded!
They had agreed that they were both big eaters, yet Darkrai had secretly been eating while hiding food away!
Too despicable!
Snorlax refused to accept it on the spot. The normally mild-tempered Snorlax was a little angry, and a little aggrieved.
He felt that Darkrai had deceived him!
Although Darkrai later traded the Energy Cubes he had stored away for a long time in exchange for Snorlax's forgiveness.
Snorlax never had another opponent for his eating contests after that.
Although Snorlax eventually realized, after his moment of anger had passed, that he should not have treated his friend that way.
He still accepted those Last Resort-grade delicious Energy Cubes.
He claimed he was saving them for Darkrai, but Lu Ze had seen Snorlax drooling over those Last Resort-grade delicious Energy Cubes more than once.
Lu Ze found it amusing. Later, he told Darkrai about it and had Darkrai pretend to discover it by accident.
In the end, following Lu Ze's instructions, Darkrai "discovered" the matter. After he and Snorlax ate all the Energy Cubes together, Snorlax finally patted his big belly in satisfaction and forgave Darkrai.
Though Darkrai's tearless, miserable expression while Lu Ze watched them eat had been quite funny.
After that, however, Darkrai's "employment fee" was greatly reduced.
Though Lu Ze