MTG Combo: Ashnod's Altar + Flayer of the Hatebound + Hex Parasite

Not exactly infinite as you need infinite black mana or infinite life to eternally trigger Hex Parasite, but that isn't really necessary since Flayer of the Hatebound has 4 power and will kill the opponent before you die usually.

The combo is simple. Sacrifice Flayer when it has no counters on it with Ashnod's Altar, triggering Undying and gaining 2 colourless mana. Flayer returns to the battlefield with a +1/+1 counter on it, dealing 5 damage to your opponent. Use one of that colourless mana and pay 2 life to activate Hex Parasite to remove a counter from Flayer. Repeat.