Jegantha does not have summoning sickness.Dean of Order.
An opponent cannot block and kill Jegantha.
Steps
Declare Jegantha and any other desired creature(s) as attackers.
Augusta triggers, as well as Najeela for each Warrior that was declared an attacker.
Resolve the Najeela trigger(s), if applicable, creating that many 1/1 Warrior creature tokens that are tapped and attacking.
Resolve the Augusta trigger, untapping all creatures you control.
Activate Jegantha by tapping it, adding ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) that cannot be spent to pay generic mana costs.
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.