The situation was as follows: an opponent had Kasmina & Saheeli and a streamer tried to Spark Harvest their Saheeli for 7 mana. Yet the program charged only 5 mana. Why could that be? Is it a bug or some rules back that?
Here is the clip: https://clips.twitch.tv/RacyTawdryZebraGOWSkull
External link →Thanks for the report, I've got a fix! The issue is mildly complicated, so bear with me for the explanation.
OrCosts check the individual options to see if the ActionCosts are payable. For example, for for Spark Harvest, it checks whether you are capable of sacrificing any creatures or planeswalkers. If you can't, it doesn't offer that option - and if there's only one option left, it auto-picks it.
Well, it turns out we weren't cleaning up those "we're determining whether this cost is payable" facts for the mana costs. And cost adjustment rules like that of Kasmina specifically check that we're not determining cost payability for them to apply.
So the fix is to clean up the DetermineCostPayability facts when checking whether an OrCost is payable. Hope that makes sense! Fix will go live with the next engine patch. #wotc_staff
This is curious. I wonder if it's a rules-handling bug generally (optional additional costs incorrectly interacting with forced additional costs) or something specific to the way Spark Harvest or Kasmina gets parsed. If a WotC dev reads this comment I'd be super interested to hear what the bug and resolution are!
I just made a reply elsewhere here, hope it's a fun read. #wotc_staff
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