What it does
Wither means that damage dealt by this creature to other creatures is dealt as -1/-1 counters instead of normal damage. So if a 3/3 with wither hits another creature, that creature gets three -1/-1 counters, permanently shrinking it rather than dealing damage that wipes at end of turn.
The most common mistake: wither only changes how damage affects creatures. Damage dealt to players, planeswalkers, or anything else is normal damage—wither doesn't make players lose -1/-1 counters or anything weird. Also, those -1/-1 counters stick around permanently and don't heal at end of turn like regular damage.
In Commander, wither is a strong combat deterrent and pairs beautifully with -1/-1 counter synergies and proliferate. It also shines against indestructible creatures, since shrinking them to 0 toughness kills them regardless of indestructibility.













