It will be especially good in decks that can use -1/-1 effects
First, at the time, we didn't let black kill black creatures
I considered playing a second Pyrite Spellbomb instead, as a lot of the time you want Pyroclasm, youre only really trying to kill one creature, and its relatively painless to draw when its bad instead of completely blank
In fact the printing of Unholy Heat (and to an extent Solitude) has mostly pushed out cards like Tarmogoyf out of the format, as the removal in the format is now so efficient that creatures either need to be one-mana, so you trade at an even level (Dragons Rage Channeler and Ragavan, Nimble Pilferer), too large to be killed by Unholy Heat (Deaths Shadow and Murktide Regent) or generate immediate value upon being played (Solitude, Fury and Omnath, Locus of Creation)
This is due in no small part to Spellstutter Sprite, one of the best counterspells-on-a-body in all of Magic