The value of X is calculated only once, as Monoist Circuit-Feeder's last ability resolves
Valakut springs to mind first as a way to deal huge bursts of damage with every subsequent land drop, but there are countless other options
Beyond just being a staple, Sephiroth, Fabled SOLDIER is perhaps the best Aristocrats card weve ever seen in MTG
Each pack contains 10 cards, with a chance of finding an Alternative Art/Secret or the coveted Manga Card
Or, if were going for sheer and utter ludicrosity, we could have the golden opportunity, with Springheart Nantuko on Mightform Harmoniser, and the Baloth Woodcrasher out, which would stack the doubling effect on each every other landfall, which would create a single Baloth which swings out as a 453,989,487,564,678,000 12 /64