What can counter Sacrifice?

Yes, Sacrifice can be countered — but the unit you killed to pay its cost stays dead.

Once Sacrifice is on the chain, any spell that counters spells works. The most efficient options:

• Defy (Calm, 1⛁) — counters it directly; same cost, same [Reaction] speed.
• Wind Wall (Calm, 3⛁) — no restrictions, counters anything.
• Hard Bargain (Chaos, 2⛁) — counters unless they pay ⛁2; they can't undo the dead unit either way.
• Abandon (Chaos, 2⛁) — counters and returns it to hand instead of trash.
• Lilting Lullaby (Calm/Mind, 2⛁, Signature) — counters and locks them out of spells for the turn.
• Riposte (Body/Order, 2⛁, Signature) — counters and buffs one of your units equal to Sacrifice's 1 Energy.

The key trade-off: per Rule 425.1.c, countering doesn't refund costs. The Mighty unit was already killed as part of paying Sacrifice's additional cost (step 4 of playing a card, before it finalizes to the chain). So you stop the draw 2 + channel, but their creature stays dead.

Two cards that won't work: Not So Fast and Repulse check whether the spell "chooses" a friendly unit. Sacrifice's "kill a friendly Mighty unit" is an additional cost, not a targeting choice (Rule 355.10.c) — so those counter spells don't interact with it.