You control a creature that can attack and that cannot be blocked and killed by an opponent.
Notable Prerequisites
Dawnsire has ten or more charge counters on it.
Steps
Declare any creature as an attacker.
Dawnsire triggers, attempting to deal 100 damage to
Crystalline Crawler, which will result in 100 +1/+1 counters being placed on it instead due to
Vigor.
Move to your postcombat main phase.
Activate
Crystalline Crawler's first ability five times by removing five +1/+1 counters from it, adding ({3} magic symbol) ({R} 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.
Repeat.
Notes
As long as
Crystalline Crawler has enough +1/+1 counters on it, you do not need to target it in step 1, allowing you to put +1/+1 counters on other creatures you control if desired.