Board Thread:Questions and Answers/@comment-152.26.192.40-20190306150941/@comment-27921889-20190306220809

If they were from packs that have random drops then your only bet is to buy them over and over to get more of them but if it is a fixed pack like the sorcery pack or the gotham pack etc. then if it comes back around again then you can buy it and promote all of the characters again. If one of the characters you have that is a challenge character, then if you're lucky enough for one of their challenges to come around, then beat it and they will be unlocked to promote from the store.