Crystalline Crawler has at least five +1/+1 counters on it.
Ornery Tumblewagg does not have summoning sickness.
Hellkite Charger and Ornery Tumblewagg 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 and Hellkite Charger as attackers.
Ornery Tumblewagg's second ability and Hellkite Charger trigger.
Resolve the Ornery Tumblewagg trigger, doubling the number of +1/+1 counters on Crystalline Crawler.
Activate Crystalline Crawler's first ability seven times by removing seven +1/+1 counters from it, adding ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Resolve the Hellkite Charger trigger, causing you to pay ({5} magic symbol) ({R} magic symbol) ({R} magic symbol) to untap all attacking creatures you control and to get an additional combat phase after this one.
Repeat from step 2.
If Crystalline Crawler begins the combo with six 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 Ornery Tumblewagg's triggers.