Najeela and Heronblade Elite do not have summoning sickness.
({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) , plus two additional mana in any two colors available.
Steps
Declare Najeela and Heronblade Elite as attackers.
Najeela triggers twice, and Heronblade Elite's myriad ability triggers.
Resolve Najeela's abilities, creating two 1/1 Warrior creature tokens that are tapped and attacking.
Resolve Heronblade Elite's myriad ability, creating two token copies of Heronblade Elite that are tapped and attacking.
The nontoken Heronblade Elite triggers twice, and each token Heronblade Elite triggers once.
Resolve all Heronblade Elite triggers, putting two +1/+1 counters on the nontoken Heronblade Elite and one +1/+1 counter on each of the token Heronblade Elites.
Activate Najeela by paying ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) ({R} magic symbol) ({G} magic symbol) , untapping all attacking creatures you control, giving them trample, lifelink, and haste until end of turn, and creating an additional combat phase after this one.
Activate the nontoken Heronblade Elite by tapping it, adding ({W} magic symbol) ({W} magic symbol) ({W} magic symbol) .
Activate a token Heronblade Elite by tapping it, adding ({U} magic symbol) ({U} magic symbol) .
Activate the other token Heronblade Elite by tapping it, adding ({B} magic symbol) ({B} 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 you control and creating an additional combat phase after this one.
Repeat from step 7, varying the colors of mana added in steps 8, 9, and 10 as needed to continue the loop.