Does wither deal damage to players in the form of -1/-1 counters or regular damage?

Wither is a keyword ability defined in CR 702.79. It changes how a source with wither deals damage to creatures: instead of marking that creature with damage, it places a number of -1/-1 counters on the creature equal to the damage dealt. This is a replacement effect that modifies the normal damage-to-creatures process.

However, wither has no effect on damage dealt to players (or planeswalkers). CR 702.79a explicitly states the ability only applies when the source deals damage to a creature. When a source with wither deals damage to a player, that damage is processed normally — the player simply loses that much life, exactly as if the source had no special ability.

This distinction matters because the game treats damage to players and damage to creatures quite differently. Damage to a creature normally results in damage marked on that creature (which can cause it to die via lethal damage), while damage to a player results in life loss. Wither replaces only the first case.

Concrete example: Your opponent controls a Quillspike (which has wither) and attacks you directly for 1 damage. You, the player, simply lose 1 life — no counters are placed on anything. If that same Quillspike had instead blocked or dealt damage to your 2/2 creature, the creature would receive one -1/-1 counter instead of having 1 damage marked on it.

So to be clear: wither = -1/-1 counters only versus creatures; regular damage versus players.