Esikas Chariot is, at absolute worst, 8/8 of stats for four mana, which almost inevitably takes two cards to remove completely
Pair it with Hinata, Dawn-Crowned, and you can target as many creatures as you like for just one red mana
Chain Reaction Terrible when there is only 1 creature on board, fantastic when there is more
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These restrictions and the "compleated" mechanic made Phyrexian mana reasonable enough to make a reappearance in Phyrexia: All Will Be One and March of the Machine , which also have a few cards with Phyrexian mana limited to the costs of activated abilities, which keeps players from actually playing cards when they can't pay their full cost in mana
The only restriction on him is that he can't get to a graveyard, which can even turn into an advantage but is necessary to guard against reanimation