Can I cast Meditation during showdown and as an attacker, exhaust my only attacking unit to draw 2?

Yes, you can cast Meditation as an attacker during a showdown and exhaust your only attacking unit to draw 2 cards.

Explanation and Sequence

According to the RiftJudge FAQ #9927, Meditation is a [Reaction] spell that allows you to exhaust a friendly unit as an additional cost to its effect.

1. State: During a showdown, the state is either "Open" (when focus is passed and no chain exists) or "Closed" (when a chain exists). Because Meditation is a [Reaction] spell, it can be played in either state.
2. Cost: When you play Meditation, you choose whether to pay the additional cost of exhausting a friendly unit. As an attacker, you control your units in that battlefield, so you may choose to exhaust your attacking unit.
3. Resolution: Because it is a [Reaction], it is placed on the chain. Per the LIFO (Last-In, First-Out) rule (Rule 342.1), the Meditation will resolve before the Showdown continues. Once it resolves, you draw 2 cards.
4. Combat Impact: Note that even though your unit becomes exhausted, it remains in the battlefield and continues to participate in the showdown. However, per Rule 414.1.c, it cannot be exhausted again, and since it is already attacking, its status as an "Attacker" is unchanged. If the unit had an ability that required it to be ready, exhausting it might prevent that ability from triggering later, but it does not remove the unit from combat.

Important Considerations:

• Controlling the Battlefield: While FAQ #10112 notes that you cannot play new units to an opponent-controlled battlefield as an attacker, you are absolutely permitted to use abilities and cast spells on the units you already have present at that location during a showdown.
• Showdown Persistence: As clarified in FAQ #8012, a showdown does not end just because a unit becomes exhausted or even if a unit dies; it continues until all players pass priority.