How do you unlock characters on sonic boom cannon 2?

buy them with rings. the lock locked characters can be unlocked by buying store items on certain days.

~ Xanadu32

Or, what you want from the store isn't available on the day your playing, just changed leave the store, change the system date, and go back in to the store. A different item will be available for each of the 31 days of the month.

- T