Its almost always used as a secondary creature type in conjunction with a more popular one (vampire horror, for example), though there are a few stand-alone horrors
They don't copy whether that creature was tapped or untapped, whether it had any counters on it, whether it had any Auras and/or Equipment attached to it, or any non-copy effects that changed its power, toughness, types, color, and so on
Most frusturatingly, perhaps, the game had a serious draw support issue, with unequal access to a strong draw engine across its several ink types
You can draw tons of cards, go wide and gradually buff your board, or make Kumena unblockable and try to knock a player out with commander damage