The only black based decks which dont play Thoughtseize at all in Modern are highly synergistic decks like Goblins or Mill, or decks which cant afford to play it due to other restrictions like Living End
Blacks aggro decks tend more towards midrange as well in the format, joining up with the other colors there with the aim to accrue value over time
Her +1 to shoot your team up and anger them into trampling over any who would dare stand in their way is also very strong, and plays well with the Wolf-making earlier
One mana for two power is very efficient, and sometimes, efficiency is all you need
Whenever you cast an instant or sorcery spell, this creature gets +4/+0 until end of turn
It can take time, but is worth it because these efficient combos really help you compete at the Pioneer power level