Here is the other concept from the google doc:
"An idea had in a thread a while back was having partners gain skills through side quests and stuff, rather than traditional leveling at a shop or blocks. This spawned an Idea for a “Koopa Bro” partner who could learn how to hurl fire, ice, boomerangs, hammers, etc. after doing quests for a fire bro, ice bro, etc. Here’s some concept art:"
The idea of partners gaining new abilities from side quests instead of shine sprites is something I think a lot of us liked and is definitely a mechanic worth taking a look at.
To build on this character, I imagine him as the youngest of the Hammer Bros., and always stuck in his older cooler brothers' shadows. He has a lot of spunk, and a motivation to get stronger than his brothers. He sympathizes with the little guy and always helps out those in need, whether they ask or not. Perhaps this in contrast to his brothers, who are evil minions. They might also be partners of another character, and every time our hammer bro accomplishes something they have already one-upped him. Eager to save the day, this hammer bro tends to rush into situations without thinking. He joins Mario after learning about Mario's quest to beat the impossibly strong baddie, perceiving this as the best way to achieve his goal of becoming the strongest hammer bro around.
In the field, he could have a high hammer toss that reaches blocks up in the air just out of reach of Mario's jump
Possible names being tossed around: Hamm, Hammah, Hambo, Stanley, Jack