Here are the Top 5 squirrel cards and, since there aren't really a ton of squirrels, the Top 5 squirrel "enablers" (cards that create squirrels without being squirrels themselves) in Magic history
Adventures in the Forgotten Realms Main Set $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 Showcase $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 Extended Arts $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 $ 0.00 Borderless $ 0.00 $ 0.00
They don't go away as steps, phases, and turns end, and effects that add mana of any type to your mana pool can't give you energy counters
Gameplay can look something like this: Turn 1: Forest, play Arboreal Grazer, put a Guildgate onto the battlefield Turn 2: Any land, cast vessel of volatility Turn 3: vessel of volatility, play Irencrag Feat into Deathbellow War Cray, summoning 2x Kragma Warcaller, 1x Rageblood Shaman, 1x fanatic of mogis
Barrier of Bones Black Oak of Odunos Blight Pile Carrion Wall Cemetery Gate Concealing Curtains Corpse Blockade Daretti, Ingenious Iconoclast Demon Wall Drift of the Dead Felothar the Steadfast Fire Navy Trebuchet Gibbering Barricade Hired Torturer Kheru Dreadmaw Moaning Wall Monoist Sentry Mordor Trebuchet Ogre Jailbreaker Oona's Gatewarden Returned Phalanx Slithering Shade Souls of the Faultless Super-Skrull Tree of Perdition Trestle Troll Wall of Blood Wall of Bone Wall of Corpses Wall of Distortion Wall of Limbs Wall of Putrid Flesh Wall of Shadows Wall of Souls Wall of Tombstones Wall of Vipers Xathrid Gorgon