Maybe Terapagos's powers would allow the MC to taste the Paradox Pokémon milk since she is somewhat linked to their creation in the timeline.
I could also see that once Terapagos gets to the ship Diancie who wants to be the most beautiful sees her Stellar Form somehow is a rival who is more beautiful without trying throws a tantrum while Terapagos is not even trying to be beautiful that it just happens and tries to not argue but it becomes a mess.
Celebi would get along great with Terapagos since both have time powers but she would find the randomness of Terapagos powers so much fun.