Board Thread:Questions and Answers/@comment-27996636-20170409221333/@comment-25031418-20170411004111

Luckless cards would cover them all, but you need to get lucky to get any given card before running out of dragon stones, tickets, or even friend points. Cards you're guaranteed to get (even if it takes multiple attempts in a mission) would be F2P/luckless cards.

Elder Kai would be a special case. You can get 50 dragon stones without paying, and it will guarantee you Elder Kai. Unlike, for example, Majin Vegeta, who you could spend 1,000 free dragon stones on and still not get. You could argue that Elder Kai is a P2P card if you had already spent all the free dragon stones, but the event is giving away more than 50, ensuring that anyone can get it guaranteed without paying.