The card wasn't completely out of flavor for green as it does have a growth theme that makes many a */* creature
But the kicker for me was the fact that when Prossh entered the battlefield, it created a bunch of 0/1 Kobold tokens

Mission: Wonder pick 1 time Reward: 1 Retro Summer (backdrop) Mission: Wonder pick 2 times Reward: 1 Yamper, Growlithe, Lillipup, Rockruff, and Fidough (backdrop) Mission: Wonder pick 3 times Reward: 1 Yamper (Pokmon coin) Mission: Wonder pick 4 times Reward: 1 Elesa (icon) Mission: Wonder pick 5 times Reward: 1 Yamper, Growlithe, Lillipup, Rockruff, and Fidough (cover) Mission: Wonder pick 7 times Reward: 1 Yamper, Growlithe, Lillipup, Rockruff, and Fidough (card sleeve) Mission: Wonder pick 8 times Reward: 1 Yamper, Growlithe, Lillipup, Rockruff, and Fidough (playmat) Mission: Wonder pick 9 times Reward: 1 Emolga (078 Promo-B) card Mission: Wonder pick 10 times Reward: 1 Growlithe (077 Promo-B) card Mission: Wonder pick 11 times Reward: 1 Emolga (078 Promo-B) card Mission: Wonder pick 12 times Reward: 1 Growlithe (077 Promo-B) card Note: Availability periods and details are subject to change without warning

Its one of the most popular partner commanders in Magic thanks to its cheap mana cost and activated ability