Ah, thanks!

By 'X', Joe means 2011 X?? I thought it was the other way around! But it makes sense why X got shorter.

The Master Emerald is essentially his Earth lol kinda fits given that it's green... :)

- Sonic's quills stand out, Knuckles quills are hanged down
- Knuckles' head is pointy whereas Sonic's head is round
- Their design emphasizes on feet and fist respectively to contrast Sonic's speed to Knuckles' strength!

One is sharp, one is rigid:
Sonic is quick, sharp, and reflexive like a blade in air
Knuckles is firm, solid, and deliberate like a pillar of stone

Sonic is sociable, Knuckles is solitary
Sonic is clever and a "fast-thinker", Knuckles is gullible and impulsive
Sonic lives in the moment, Knuckles lives for his duty
Sonic runs from the past, Knuckles is bound by it

Wind erodes the mountain, but the mountain also shapes the wind

Both have rather ironic fears, Sonic is afraid of deep water (not aquaphobic!) even though hedgehogs knows how to swim and Knuckles hates strong sunlight even though echidnas actually love sunlight

Sonic is a hedgehog. In Japanese, hedgehogs are called “harinezumi/needlemouse”. Sonic Team wanted another “needle” character so they made Knuckles and echidna which are called “Harimogura/needlemole[s]” in Japanese.

Both Sonic and Knuckles have black influence in their designs! Sonic’s boots were inspired by Santa Claus + Michael Jackson while Knuckles has shoes that were inspired by the Rasta flag and has dreadlocks!

Sonic is also the wind to Knuckles' mountain, being described as fast and free like the wind, going wherever he goes while Knuckles is rooted in one place like a mountain.

Sonic is the sun! He has a circular chest which resembles the sun in contrast to Knuckles being the moon, having a moon crescent chest

Knuckles is Sonic's balance in the same way the moon is to the sun! We use our hearts to power Super Sonic (a star!), Knuckle protects and regulates power (M.E)

Design-wise, they contrast a lot(!):
Sonic: long nose/Knuckles: short nose
Sonic: round eyes/Knuckles: sharp eyes Sonic: short muzzle/Knuckles: long muzzle:
Image by @ckforbesX and @FlameZ_yuh