Sacrifice it for a damage, return it to your hand, replay it for no mana, and then repeat until everyone has died
It turns out that when you effectively tack on draw a card to anything that costs 1 mana and also powers up your aggressive creatures, you get a damn powerful deck
This card was broken upon its release so much so that it was retroactively added to the previous ban list that was released by Wizards of the Coast before the set that spawned it (Urzas Legacy) debuted
As Ive mentioned previously, you run into a lot of situations where Collar would be a good card to tutor up, but you have a Chalice of the Void with one counter on the battlefield and then you feel sad
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Against four or five, you will likely be getting many in any color out of this