Do you really have to defeat the elite four 100 times for mystic ticket?

You are likely thinking of a game like Pokémon Brilliant Diamond and Shining Pearl. In these games, you do not need to defeat the Elite Four 100 times to get the Mystic Ticket.

Here's how you actually get the Mystic Ticket:

1. Complete the main story: Beat the Elite Four and become the champion.

2. Talk to the Lake Guardians: After becoming champion, you can talk to the three Lake Guardians (Uxie, Mesprit, and Azelf) in their respective lakes.

3. Speak to the Lake Guardians again: After talking to the Lake Guardians once, return to the same spots again to be given the Mystic Ticket.

So, no, you don't have to defeat the Elite Four 100 times! It's a much simpler process.