Opponents can not block and kill creatures you control.
Steps
At the beginning of your combat phase, Helm of the Host triggers, creating a token copy of Jegantha with haste that isn't legendary.
Activate the Jegantha token 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.