Simply unheard of.
Gigantamax did not actually make Pokémon grow larger out of thin air, Calyrex explained.
The Gigantamax Pokémon you see are merely projections formed from solidified energy. Once the energy is exhausted or they are defeated, the energy projections shatter, creating a chain-explosion phenomenon. In other words, there is no side effect that prevents Pokémon from evolving.
This matched what Roy knew. He asked in confusion, "Then what's going on with this Shelgon?" This involved Shelgon's own traits. Calyrex displayed Its vast knowledge. It had read plenty of the Pokémon League's Pokédexes and could recite them backward and forward.
The Shelgon stage was similar to the cocoon stages of Pokémon like Kakuna and Metapod. Within its hard shell, its cells were constantly changing, nurturing a brand-new body... You could regard it as a Dragonite body being nurtured inside the shell.
Roy understood instantly upon hearing that.
During such a critical period of rapid cellular change, frequent exposure to Gigantamax Energy would inevitably have an effect.
To use a somewhat inappropriate analogy, pregnant women knew they could not be exposed to excessive radiation during pregnancy, or it could cause fetal deformities.
The reason this Shelgon could not evolve was because it had been exposed to Gigantamax Energy radiation during its developmental stage, and something had gone wrong. As for exactly what had gone wrong...
Roy suddenly realized something and asked, "Wait, you said it's very large... How large?"
Calyrex turned to look at Roy. Its expression remained calm, but there was a hint of satisfaction in Its eyes.
...Had he realized it?
By your human units of measurement, it stood roughly 3.5 meters tall.
Roy was speechless.
Shelgon's average height was 1.1 meters. The Dragonite it would nurture was only around 1.5 meters tall.
This Shelgon was more than