Areon, Luminescent Traveler

When Areon, Luminating Traveler enters the
battlefield remove all counters from
permanents and players.
Whenever one or more -1/-1 counters would
be placed on a creature you control, Areon,
Luminescent Traveler puts that much +1/+1
counters on that creature instead.
Only counters placed by Areon, Luminescent
Traveler can be placed on permanents.