Creature with MV<=1 that enters the battlefield with a +1/+1 counter on it
Initial Card State
Creature with MV<=1 that enters the battlefield with a +1/+1 counter on it in hand.
All other permanents on the battlefield.
Notable Prerequisites
You have enough mana to cast the creature with MV<=1 if it doesn't have ({X} magic symbol) in its mana cost, or ({1} magic symbol) available otherwise.
Steps
Cast the creature with MV<=1 by paying its mana cost if it doesn't have ({X} magic symbol) in its mana cost, or by paying ({1} magic symbol) otherwise, causing the creature to enter the battlefield with a +1/+1 counter on it.
Activate
Phyrexian Altar by sacrificing the creature, adding ({1} magic symbol) .
When the creature dies,
Reyhan triggers, putting a +1/+1 counter on
Evolution Witness.
Evolution Witness triggers, returning the creature from your graveyard to your hand.
Repeat.
Results
Infinite +1/+1 counters on a creature.
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite sacrifice triggers.
Infinite storm count.
Metadata
In 482 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Exhibition (Bracket 1+).