The downside is youre limited to cards that actually have the printed madness ability, with only a few ways to apply that ability to other cards
Menace is a great keyword to pair with the attack trigger, forcing two blockers from opponents and generally making sure these two brothers can safely get in the zone and provide value
Shifting this Peter Pan onto another gets him into play earlier, making it much easier to challenge characters and control the board
Dragons of Tarkir gave us five newcomers (Dragonlord Silumgar, Dragonlord Atarka, etc.), Core Set 2019 gave us retrains of the originals (Arcades, the Strategist, Nicol Bolas, the Ravager), Strixhaven added five more as the namesakes of the different schools (Tanazir Quandrix, Beledros Witherbloom, etc.), and the five metal dragons from Baldur's Gate were also given the double creature type (Ancient Bronze Dragon, Ancient Copper Dragon, etc.)
Nongreen two-color decks welcome this mana ramp and color fixing at just two mana