I find it strange that a planet upgrades into a sun.
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As for the card, it's interesting. "Red Sun" makes me think of Gravity and Fire synergy.. So, since there already is a bond between the two, is there a possibility of adding a Fire quanta production ability to the upgraded version and making the unupgraded version only produce Gravity? That way, both converts quanta into Gravity and the Sun makes Fire as well. I know it collides in a way, but maybe that can be dealt with by omitting Fire with the conversion?
Edit: I saw your posts in Kael Hate's Terracavern thread.
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I don't mean the combination in a way that Gravity is special, just that you mentioned it not working in mono-gravity, which made me think of Multiple Firemasters on the field.