Rounding out the mana rocks, Id like to suggest two that I think will always make the shortlist: Chromatic Lantern, and Thran Dynamo
(2017-04-18) If a spell has no mana cost, its mana value is 0
Darksteel Reactor Darksteel Reactor is the epitome of an Against the Odds card, and even then, 20 counters is asking a lotso much so than when we played it in Modern, we cheated by turning it into an indestructible creature to beat down with, rather than trying to win by getting 20 charge counters on it
Eiscue ex leaps into the air, with the candelabra-shaped Tera crystal on its head facing outward and emitting flames
True to her sly fox form, Madam Mim, Fox has the Rush keyword, letting the card challenge on the same turn its played - making that five strength a great way to spring a surprise ambush on your opponents