Activate Saheeli by paying 2 and tapping it, creating a token copy of Little Bear with haste.
When the token Little Bear enters the battlefield, it and Mana Echoes trigger.
Resolve the Little Bear trigger, untapping Saheeli.
Resolve the Mana Echoes trigger, adding C for each creature you control that shares a creature type with Little Bear.
Repeat.
This delightful concoction turns a humble cub into an endless engine of creation, all made possible by Mycosynth Lattice turning every permanent into an artifact so Saheeli, the Sun's Brilliance can copy anything on your board—including Little Bear. Because Little Bear enters with flash and triggers its own untap ability upon arrival, it instantly refreshes Saheeli for another go-around. Meanwhile, Mana Echoes watches each new token flood the battlefield and rewards your growing menagerie with a mounting wave of color-fixing mana, easily sustaining the loop and fueling an infinite army of hasty tokens.