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If Shimmerwilds Growth is somehow on the battlefield without a chosen color, its last ability won't add any mana
Mythos of Snapdax also tends to whiff if your opponents control more than one each of those permanents types
Core sets always had the issue that they werent as popular with players as other Standard sets, often lacking a creative theme for players to get excited about, or just not having many new cards
From there its suit-to-taste, but it seems like Boldwyr Intimidator makes excellent use of the mana from your commanders triggered ability, turning up to two creatures into Cowards, who then cant block
And if Kozilek dies you just play more mana rocks, casting Kozilek, and refill your hand again