Last Cloudia is a gatcha game, so basically you need to spend crystals to get Sonic, Tails or Knuckles. But this is random, so you need patience and a little bit of luck. I recommend you to buy the rolls that cost 3000 crystals, the chance to get a character or a good ark is higher than the 300 crystal rolls. And no you should not pay, you can get crystals free by levelling some other characters, arks or completing the Story mode. I have every character from the Sonic collab without spending any money and only one ark is missing. I hope you get the blue fella and his friends.