In this deck, the Great Stone Dragon actually ends up being phenomenally effective
It's definitely doable, but it does make this less good
Its a fine Rampant Growth variant that can Fog a creature by blocking then sacrificing itself, giving it some late game relevance
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Darkness Crystal's first ability)
In terms of cost and vulnerability Baneslayer and Wurmcoil are fairly comparable
You can copy a fetch land to ramp out a bunch of lands at once, or copy a game-winning ability to end the game in a wild way