Back before magicthegathering.com existed, there was a site (and print magazine) run by Wizards of the Coast called The Sideboard that featured strategy written by some of Magics top pros
The coolest thing that Ive seen someone do with March of Swirling Mist is exiling their Misthollow Griffin and phasing out some of my hatebears so that they could go off with Food Chain by casting the Misthollow Griffin from exile
The card really felt like you had to restrain this creature with mana, tying him to your will or he would trample loose like the badass he is
Sylvan Library is a natural addition as well if splashing another color, as this not only helps smooth out draws, but it has additional synergy with Howling Mine, digging deeper with each draw step
Your Choice
Both Maja, Bretagard ProtectorMaja, Bretagard Protector and SporemoundSporemound create tokens when a land enters the battlefield, with Maja going the distance and even buffing those creatures as well