None of the involved permanents have summoning sickness.
Opponents can not block and kill creatures you control.
Steps
Declare
Najeela,
Ahn-Crop Champion and
Jegantha as attackers, choosing to exert
Ahn-Crop Champion as it attacks.
Ahn-Crop Champion and
Najeela trigger.
Resolve the
Ahn-Crop Champion trigger, untapping all other creatures you control.
Resolve the
Najeela trigger, creating a 1/1 Warrior creature token that's tapped and attacking.
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.
Repeat each combat phase.
Results
Infinite combat phases.
Infinite creature tokens.
Infinite ETB.
Infinite lifegain.
Infinite lifegain triggers.
Metadata
In 46 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Exhibition (Bracket 1+).