We asked the ReFoReMo Facebook group which mentor texts taught them the most about great picture book writing as a whole and why? Here's the list of 2016 books the group responded with.
For poetry:

For non-fiction narratives:
The William Hoy Story by Nancy Churnin and Jez Tuya
The Hole Story of the Doughnut by Pat Miller and Vincent X. Kirsch
Seven and a Half Tons of Steel by Janet Nolan and Thomas Gonzalez
On the Farm at the Market by G. Brian Karas
Coyote Moon by Maria Gianferrari and Bagram Ibatoulline

For tight writing and humor:
Mary had a little Glam, by Tami Sauer and Vanessa Brantley Newton
I Love Cake!:Starring Rabbit Porcupine and Moose by Tammi Sauer and Angie Rozelaar
Horrible Bear! by Ame Dyckman
For friendship and emotional resonance:
Ida Always by Caron Levis
Too Many Carrots by Katy Hudson
For diversity:
A Piece of Home by Jeri Watts and Hyewon Yum
For unique point of view:
A Tree in the Courtyard: Looking Through Anne Frank's Window by Jeff Gottesfeld.
For literary appeal and illustrations:
The Night Gardener by The Fan Brothers
Thank you to the ReFoReMo Facebookers that contributed to this list!
What picture books did you use as mentor texts this year and why?