If I control Vizier of Remedies and Winding Constrictor, and something tries to put a -1/-1 counter on one of my creatures, what happens?
You choose the order in which the effects will be applied.
The order doesn’t matter if the effect would put two or more -1/-1 counters on the creature, since both effects will still end up applying and cancel each other out and the creature will just get the normal amount of -1/-1 counters.
If the effect would put exactly one -1/-1 counter on the creature, then applying Vizier of Remedies’ effect first will mean that the effect is no longer placing any counters and thus Winding Constrictor’s effect will no longer be applicable. Applying Winding Constrictor’s effect first will change the one counter into two and then Vizier will knock it back down to one.