The intentional including of some weaker, not-on-theme cards for the reprint machine, like Brilliant Plan, Kongming, "Sleeping Dragon", or newer cards that weren't on theme like Tidal Force are the only things keeping the synergy from your deck from breaking people in the face unfairly
Maushold ex from Paradox Rift is a great centerpiece card, and there are enough variants across sets to keep it interesting
And theres Swarmyard MassacreSwarmyard Massacre, a five-mana sorcery that gives us two Squirrel tokens and then gives all creatures that arent Squirrels, Rats, Insects, and Spiders -1/-1 for each Squirrel, Rat, Insect, and Spider we control
Beyond this, however, just dealing damage with Scurry of Squirrels will also let you buff your board
Note that I am only including cards that milled for the sake of milling, not cards that happen to put a card or two into the graveyard while accomplishing some other task