"Weapons that inflict Explosive Damage (X) gain a bonus against Hordes, and count as having inflicted one additional Hit per Attack after all other Hits have been applied"

The wording of this is confusing. It says you gain a bonus, and then goes on to state that it counts as inflicting extra hits, but it never states what the bonus is. Is the bonus that it inflicts additional hits? and if that is the case, why include "and". "and" implies that it gains a bonus in addition to the first bonus, not that it's explaining the mention in the first half of the sentence.

The bonus is that inflicts an extra hit. Regardless of the wording, that is how it works.

"Weapons that inflict Explosive Damage (X) gain a bonus against Hordes, and count as having inflicted one additional Hit per Attack after all other Hits have been applied"

The first section of the sentance states you gain a bonus. The second section of the sentance then explains what that bonus is. This sentance is not saying, "theres a bonus in addition to on extra hit." The proof is the comma, which in this case indicates a compound sentance. A compound sentance is essentially two sentances in one. In this example the second 'sentance' is expanding on the subject matter of the first.

If the sentance meant, "you get a bonus and inflict an extra hit," it would have read, "Weapons that inflict Explosive Damage (X) gain a bonus against Hordes and count as having inflicted one additional Hit per Attack after all other Hits have been applied." Notice in this sentance there is no comma.

According to correct reading of English there is no implication of an "additional" bonus.