These are the legends, like the Power 9, which includes the undisputed king Black Lotus, and the 10 original dual lands like Underground Sea and Volcanic Island
Most builds lean into that momentum to draw your whole deck with something like Soul of the Harvest and then seal the deal with a finisher like Purphoros, God of the Forge
Costing only three mana (1B, 1G, 1C) and entering play as a 3/4 with Deathtouch makes it very impactful
There are also several other takes on this piece featuring different Pokemon Eevee, Psyduck, Rowlet, and Mimikyu
Some back faces have abilities that allow them to transform back to their front faces, but for back faces like Hades, it's a one-way journey, although some other spells and abilities may still cause it to transform back