Ranger Mason is the Character of the Day in Mother of All Battles and is the ranger in charge of the Mt. Silver Pokémon Preserve, the same preserve Ash's Larvitar was stolen from.
After meeting Ash and company, she teamed up with them to stop any more poaching in the preserve. When the poachers were defeated by Larvitar's mother, Tyranitar, Mason captured the poachers and thanked Ash and friends before they departed for the Silver Conference.
It was first seen riding on the back of her motorcycle when Mason came to help Ash and friends, who were under attack from the poachers.
This is the mother of the Larvitar Ash held on to temporarily. In the dimension, Tyranitar was seen fighting poachers, receiving a scar in the process, before Lavitar's egg was stolen by the poachers. She mistakenly assumes Ash and friends are poachers until Larvitar calms her down. But the poachers from Larvitar's memories appear and capture Tyranitar.
Larvitar was entrusted to Ash by Professor Elm as an egg. After a rough hatching, where its shell was cold, it hatched but was afraid others, causing it to use Screech to drive them away or by freezing in fear. Slowly, it opened up to only Ash, but after helping it get past its emotional scars, it opened up to Ash's friends. After being reunited with its mother, it said goodbye to Ash and company.