Crystalline Crawler without summoning sickness and
Arcbound Overseer with five or more +1/+1 counters on it).
Notable Prerequisites
Alesha cannot be blocked and killed by an opponent.
Mana Needed
({WB} magic symbol) ({WB} magic symbol) available available.
Steps
Activate
Crystalline Crawler's second ability by tapping it, putting a +1/+1 counter on it.
Activate
Phyrexian Altar by sacrificing
Arcbound Overseer, adding ({R} magic symbol) .
When
Arcbound Overseer dies, it triggers, putting its +1/+1 counters on
Crystalline Crawler.
Activate
Crystalline Crawler's first ability four times by removing four +1/+1 counters from it, adding ({3} magic symbol) ({R} magic symbol) .
Activate
Aggravated Assault by paying ({3} magic symbol) ({R} magic symbol) ({R} magic symbol) , causing you to untap all creatures you control and to get an additional combat and main phase after this one.
Declare
Alesha as an attacker, triggering its ability, targeting
Arcbound Overseer.
Activate
Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding ({WB} magic symbol) ({WB} magic symbol) .
Resolve the
Alesha trigger, causing you to pay ({WB} magic symbol) ({WB} magic symbol) to return
Arcbound Overseer from your graveyard to the battlefield tapped and attacking with six +1/+1 counters on it due to its modular ability.
Repeat.
Results
Infinite LTB.
Infinite ETB.
Infinite colored mana.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite combat phases.
Infinite untap of creatures you control.
Infinite mana creatures you control can produce.
Infinite +1/+1 counters on artifact creatures you control.