When Toshiro Umezawa was first spoiled (showing my age here) I was very excited about the card. As things played out, his Jitte ended up stealing the show, but Toshiro remains a pretty sweet design, and Tiny Leaders is the ideal format to put the old Samurai to work.
There are certain leaders that will make taking full advantage of Toshiro difficult. Geist of Saint Traft comes to mind. Forbidden Orchard is an option for Toshiro decks to give you something to kill, but then you also need to expend resources to kill the spirit tokens. Instead I like just filling up on a few choice removal spells and a bunch of great card advantage spells.
This is my current list for Toshiro Umezawa:
The deck is a little light on win conditions and is definitely on the suicidal side, but the interactions are sweet. Mimic Vat and Fleshbag Marauder is a pretty nice little combo that only gets better with an active Toshiro.
The sideboard for this deck needs to be dedicated to “correcting” matchups. The edits here are great, but very lack-luster against Elves or Goblins, so having access to cards like Shrivel and Drown in Sorrow is a must.