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 and
Najeela, if desired, as an attacker.
Ornery Tumblewagg's second ability triggers, doubling the number of +1/+1 counters on
Crystalline Crawler.
If
Najeela was declared as an attacker, it triggers, creating a 1/1 Warrior creature token that is tapped and attacking.
Activate
Crystalline Crawler's first ability five times by removing five +1/+1 counters from it, adding ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) .
Activate
Najeela by paying ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) , untapping all attacking creatures, giving them trample, lifelink and haste, and gaining an additional combat 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