Does wither damage use -1/-1 counters instead of regular damage, and do those counters stay after the damage is dealt?

Wither is a static ability that changes how damage is dealt to creatures. Normally, damage dealt to a creature is tracked as 'damage marked on that creature' and is removed at end of turn (CR 119.3). Wither overrides this: any damage dealt to a creature by a source with wither is instead dealt in the form of -1/-1 counters placed on that creature (CR 702.79a).

Because -1/-1 counters are placed on the creature rather than damage being 'marked,' the effect is permanent. Counters are not removed at end of turn — they stay on the creature until something specifically removes them (CR 122.1). This means even a creature that survives the hit is permanently weakened.

It is important to note that wither only changes how damage is applied to creatures. If the source with wither deals damage to a player or planeswalker, that damage is handled normally (as life loss or loyalty loss), not as counters.

Concrete example: You attack with％Rendclaw Trow (a 2/2 with wither). Your opponent blocks with a 4/4 creature. The Trow deals 2 damage to the 4/4, but instead of marking 2 damage, two -1/-1 counters are placed on the 4/4. It becomes a 2/2 permanently. Next turn, it is still a 2/2 — the counters did not go away at end of turn.

Referenced rules: CR 702.79a (wither definition), CR 119.3 (damage removal at end of turn), CR 122.1 (counters on permanents).