You'd be legitimately surprised at how many common lands end up seeing play in Pauper, purely because most of them suck out of control.
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On a
slightly different topic...
A cube where mana of one particular color is paid for by gaining poison counters instead of through spending mana is... intriguing. What does the design/play experience look like when each player is capped at spending nine of a given color of mana?
I envision it being a four color cube with gold cards sprinkled throughout. Oh, sure, the white section looks normal... but then there's a two-mana mono-white
Vindicate that just asks you to let in a
little bit of corruption. Or you have a normal blue section with a one-mana
Growth Spiral peaking through and asking you for to let a bit of the beast spirit in...
You'd need something to give it a bit more
bite, but the idea's kinda evocative.