Jax, Unrelenting

Jax, Unrelenting — Unit/Champion, Body, 4 Energy + 1 Power, 3 Might, with Weaponmaster and Equip:

"[Weaponmaster] (When you play me, you may [Equip] one of your Equipment to me for [A] less, even if it's already attached.) When you attach an Equipment to me, you may pay [1] to draw 1."

Two things to keep straight. Weaponmaster only functions as a play trigger — it has no function while Jax is on the board (Rule 821.2), so it can't be re-used later, and the [A] discount only reduces the any-domain power portion of an Equip cost (it can still pick an Equipment with no [A] in its cost, just unreduced, Rule 821.1.c.3–.4). You can also pick an Equipment that's already attached to another unit and move it.

The second ability is separate and triggers on any attach to Jax — Weaponmaster, an Equip activation, or a legend ability like Grandmaster at Arms. Each attach triggers it separately, and since it's a triggered ability you choose whether to pay the [1] when it resolves on the chain, not when it triggers. No errata on this card.