Emerald Oracle said:
Does the whole Flag thing have any actual in-game Reward? Or is it just another fun little thing to do for its own sake like trying to complete a pokedex?
Bronze: 10 Flags will net you a Blackboard you can write on, additional items in the Secret Base Headquarters that you can buy and an additional skill your secret base pals can use.
Silver: 100 Flags will net you a Juke Box decoration, more items in the Secret Base Headquaters to buy, and a third skill your secret Base pals can use.
Gold: 500 Flags will net you a Mood Lighting decoration, more items that you can buy at the Headquarters as well as being able to take a picture of the current team in your base at any time, and a fourth skill your secret base pals can use.
Platinum: 1000 Flags will net you a Confetti Ball decoration, a
Garchompite, and allow you to use 2 skills per day from each of your secret base pals.
You do have to talk to Arune every time you reach the limit of each level to gain the new things that each new flag level brings.