bone skewer ignores addcional costs to?

Yes — Bone Skewer wipes out additional costs too.

Its text says the unit is played "ignoring any and all costs," which is the strongest wording the rules use: it sets the Total Cost to 0, including non-standard/additional costs (Rule 356.5.a). So if the chosen unit has a mandatory cost like "As an additional cost to play me, kill a friendly unit" or "pay [C]...", that cost is not paid — the unit just enters play.

This is different from cards like Baited Hook that only say "ignoring its cost," which zero out base Energy/Power but still require any additional costs (FAQs 7296/2488). Bone Skewer's "any and all" language goes further. Note: since Deflect only exists on permanents on the battlefield, it never applies to units being played from hand anyway (FAQ 8683) — but even if it did, Bone Skewer's wording would still ignore it.