Isshin, Two Heavens as One

If a creature attacking causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Rainbow Dash

Flying, haste
Whenever a creature you control with flying and/or haste attacks, you get 20% cooler. (You start at 0% coolness.)
Sonic Rainboom — {T}: If you're at least 100% cool, add {W}{U}{B}{R}{G}, draw a card, and reset your coolness.

Najeela, the Blade-Blossom

Whenever a Warrior attacks, you may have its controller create a 1/1 white Warrior creature token that's tapped and attacking.
{W}{U}{B}{R}{G}: Untap all attacking creatures. They gain trample, lifelink, and haste until end of turn. After this phase, there is an additional combat phase. Activate only during combat.