There seems to a lot of interest in the format, as many cards have seen prices surges and there’s a lot of discussion. So, I’m just throwing a few more ideas out there.
Isamaru is not legal, but we have some other one mana legendary creatures, so why not do something with that? (Because it’s not going to be good, but don’t worry, that’s not my first thought.)
The first Pioneer leagues seemed like aggro would be strong and many of the first brews were combos. What to do? Especially, if one of those strong decks turned out to be GW Hexproof? Maybe something like this:
Breaking away from Mardu, maybe some tribal action? Zombies? It was a strong standard deck, which even won a PT, so it might be even better with a few additions. There’s actually probably many ways you could build this. You could be faster or more midrange-y. You could get very grindy with Midnight Reaper, for example.