emerald000

That's pretty much what I had in mind.

I was actually considering something similar as an upgrade to the current deck archetype system. Once the archetype system is working well and has most archetypes/variants included, this is somewhat...

Retrace is an additional cost, not an alternative cost. You are able to retrace a spell without paying its mana cost (by discarding a land) with Fires of Invention.

West of the southeasternmost lake in Feldip Hills. 

If multiple effects allow you to cast a spell, you have to choose which effect you are using. Therefore with those two cards on the battlefield, you may either cast...

It's probably better to add a flag to abilities that care about which colours you use. There are other cards such as Firespout and friends, and the Adamant ability.