Quickdraw creatures
I posted a new keyword I came up with "Quickdraw" a few weeks ago, with the idea of being able to cast spells at instant speed for an alternate cost. Each of the alternate costs was simply an extra tax, and there were people confused as to why even have a keyword. I had the ultimate idea of having completely alternate casting costs, potentially even making it cheaper with flash than without.
Here is a cycle of creatures that I think covers quite a good range of what this keyword's potential is, and the modality of what it could offer.