I'm having a problem with the Madness keyword. I discarded
Basking Rootwalla to
Survival of the Fittest. Madness triggers on
Basking Rootwalla, and it asks if I want to use the ability. I choose Yes, then the card goes to exile. I am not asked to pay the Madness cost (in this case 0 mana). Then at the end of the current phase, the
Basking Rootwalla is moved from exile to the graveyard, saying its Madness cost wasn't paid.
I haven't tried other Madness cards to see how they are working. It's possible that
Basking Rootwalla's problem is that the Madness cost is 0, so it doesn't know how to handle the payment part. Otherwise maybe Madness isn't asking for the payment at all.
The other thing to look at is that you should only be able to pay the Madness cost the very next time you have priority. When using it here, the
Basking Rootwalla was going to the graveyard at the end of the current phase, but if the Madness cost isn't paid, it should go to the graveyard before other things on the stack are resolved (in my case the
Survival of the Fittest ability).
Relevant rule:
502.24c Any time you discard a card which has madness, you have the option to remove it from the game (to play it using its madness ability) or not. If you remove it from the game, the second part of the madness ability triggers. When this ability resolves, you have the option of playing the spell for its madness cost. You can only play it the very next time you could play an instant this turn. If it's an instant or sorcery, put it into your graveyard when it resolves. If it's an artifact, creature or enchantment, put it into play when it resolves.
https://github.com/magefree/mage/issues/554FIXED