When you spend your berries, play it more than once. What I mean is that when you finish once choose a different Pokemon or play again with the same Pokemon so you would not have to spend more berries to play it
1: Double Double Dash - After a double dash, and after the Sound Effect is finished, you can press ② To dash again. Its hard, but eventually you can keep dashing.
2: The Rainbow: After you beat the game, if you make all 193 friends, you can eventually go to Mew in the Sky Pavillion, and see the true ending. Spoiler:
It's all the "main" characters come to celebrate, Not that great.
click to reveal
3: Getting 99,999 on Bastidon's Panel Crush: Even if you don't have Metagross, it's really easy. Just keep pressing 2 when the ball comes your way, and It'll pass over Dugtrio, and past Bastiodon. I accomplishes it with a Pikachu.