Board Thread:Questions and Answers/@comment-29328744-20161103010711/@comment-29865957-20170111020735

If you want to maximize your DS, I'd just save everything for discount multis (I seem to recall seeing a discount single once, but even if it happened, it's super rare). More characters per stone is the best odds you've got. Especially considering multis are (from what I can tell) calculated as 10 single summons.