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This is a stupid idea I've been having to make a card like Chord of Calling work with manual mana abilities only (i.e., non-AI). Would it be possible to modify the code of Springleaf Drum so that you could tap any number of untapped creatures you control, add one mana of any color to your mana pool for each creature tapped in this way, and then have this be an additional cost for a card? I don't know if this would be even possible or feasible, but it might be worth a shot.

The problem with Chord of Calling is the cost. The engine won't let you select a value for greater than the mana you have available. This is a problem with convoke since convoke allows you to do that very thing.


Maybe you could approximate it if you removed the cost and did that part manually. That is, is an activated ability to set the value of X while it is in your hand and then adjust the cost of the card (like Thalia adjusts the cost of cards). Of course this wouldn't work in all cases but it's a start of an approximation. And it also works poorly with cards that need to know the CMC.

Convoke has several problems being implemented (and I've gone over them before, including a proof of concept for DotP 2013 which is still flawed but works, so I'm not going to do it yet again) and having an in the casting cost causes even further problems (which can't be solved by my approximation for DotP 2013).