Animar, Soul of the Elements feels like the most obvious choice, synergizing extremely well with all of the high-cost creatures in this deck while also resisting common targeted removal
This can easily be exploited with untap effects like Arbor Elf, to produce a ton of mana in a single turn
it also finished second at Championship Finals Yokohama
Leyline of the Guildpact has some utility in Commander too, where cards like The Mana Rig, Fallaji Wayfarer, Hero of Precinct One, and Rienne, Angel of Rebirth might fit together with the Leyline in a Jenson Carthalion, Druid Exile deck
For example, a card like Sandwurm Convergence says you cant be attacked by fliers, but that protection doesnt extend to your partner, so your opponents can just send all their flying attackers at your partner for the same effect
Ambassador Blorpityblorpboop has received a minor update to clarify its function