As for the others, a doubling of mana cost would still leave you with absurd cards, UU - Draw 3
It saw a slight increase due to the Enchantment support in the Kamigawa: Neon Dynasty set that grew its value to around $9
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Two creatures in one turn is not very hard to do in cube at all
That ability is "when the last defense counter is removed from this permanent, exile it, then you may cast it transformed without paying its mana cost." This means that if for any reason a battle enters the battlefield without defense counters, it will be put into the graveyard and its controller will not get the chance to exile it
The card maintains that potential in the right Cube, and its also useful in casual Commander as a cheapish way to draw a card and reset a graveyard, be it yours or somebody elses