Companion — Each creature card in your starting deck is a Cat, Elemental, Nightmare, Dinosaur, or Beast card. (If this card is your chosen companion, you may put it into your hand from outside the game for as a sorcery.)
Each other creature you control that's a Cat, Elemental, Nightmare, Dinosaur, or Beast gets +1/+1 and has vigilance.
Kaheera helms a creature-heavy GW midrange/aggro deck built almost entirely from Cats, Elementals, Nightmares, Dinosaurs, and Beasts, who all get +1/+1 and vigilance. You deploy efficient typal creatures, anthem your board, and attack with vigilant beaters that still hold the fort. Lean on green ramp and white removal/protection to grind to a wide, sticky board that closes games through combat.
Free anthem on a 3-mana commander that buffs and grants vigilance, letting you attack without dropping defense
Vigilance synergizes with tap-to-attack payoffs, blockers, and convoke effects
GW gives premier ramp, go-wide tokens, and clean removal/protection
Tribal flexibility — five creature types cover a huge swath of strong green/white creatures
Buff only applies to the five chosen types, so off-type utility creatures miss out
No inherent card advantage or recursion engine built into the commander
Board wipes hit hard since the strategy is creature-dependent
Lacks evasion and reach; ground stalls and fliers can stonewall the plan
Legendary Creature — Cat Beast
as a sorcery.)