Crystalline Crawler has at least three +1/+1 counters on it.
Ornery Tumblewagg does not have summoning sickness and cannot be blocked and killed by an opponent.
Steps
Activate
Ornery Tumblewagg's saddle ability by tapping
Crystalline Crawler, causing
Ornery Tumblewagg to become saddled until end of turn.
At the beginning of your combat phase,
Ornery Tumblewagg's first ability triggers, putting a +1/+1 counter on
Crystalline Crawler.
Declare
Ornery Tumblewagg as an attacker.
Ornery Tumblewagg's second ability triggers, doubling the number of +1/+1 counters on
Crystalline Crawler.
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 from step 2.
If
Crystalline Crawler begins the combo with four or more +1/+1 counters, this combo will net infinite +1/+1 counters on it and colored mana, which will allow you to target any other creature(s) using