In FFXIV, you fight him on that green circle you see in the card, and one of his abilities more or less cuts the stage in half, thus the trigger
Before we begin, lets divide Avatar cards into two sets: Avatar: The Last Airbender (TLA) is the main Avatar Standard-legal set, with around 300 different cards
There are tons of extremely powerful effects that become even better when doubled up, like Portal to Phyrexia's ability to force your opponents to sacrifice three creatures when it comes into play, now forcing all your opponents to sacrifice six creatures instead

Julius Jumblemorph Ego Erasure Feisty Spikeling Firdoch Core Fire-Belly Changeling Flock Impostor Formless Genesis Game-Trail Changeling Gangly Stompling Ghostly Changeling Gladewalker Ritualist Graveshifter Guardian Gladewalker Impostor of the Sixth Pride Irregular Cohort Littjara Littjara Glade-Warden Littjara Kinseekers Masked Vandal Maskwood Nexus Mirror Entity Mischievous Sneakling Mistform Ultimus Mistwalker Moonglove Changeling Moritte of the Frost Morophon, the Boundless Mothdust Changeling Mutable Explorer Nameless Inversion Omni-Changeling Omo, Queen of Vesuva Overlord of the Hauntwoods Personify Prideful Feastling Realmwalker Rooftop Percher Runed Stalactite Shapesharer Shields of Velis Vel Sizzling Changeling Skeletal Changeling Springleaf Parade Stalactite Dagger Taurean Mauler Three Tree Mascot Turtleshell Changeling Universal Automaton Unsettled Mariner Valiant Changeling

Imagine playing this, dropping Myojin of Life's Web, and then next turn using Garruks first ability and drawing two creatures and using Myojin to drop all of your creatures into play
When things are not perfect the simple Whisper does well