Via the Steam Community:

Diretide

Penguin

• Max Speed: 700 -> 750
• Turn Rate Max: 120 -> 130
• Post Crash Speed: 100 -> half of pre-crash speed, min 100
• Post Crash Turn Rate: x1.5 normal turn rate for 2s

Ogre Seal

• Impact Radius: 200 -> 250
• Damage Per Level: 15 -> 25
• Hops 2 more times after dismount

Snowball

• Acceleration: 150 -> 200
• Post Crash Speed: 100 -> half of pre-crash speed, min 100
• Post Crash Turn Rate: x1.5 for 2s

Frosted Toad

• Hop Time: 0.55s -> O.45s
• Hop Pause Time: 0.5s -> 0.85s
• Turn Rate: 230 -> 150
• Impact Radius: 300 -> 175
• Damage Per Level: 12 -> 8
• Knockback Distance: 125 -> 75
• Knockback Duration: 0.3s -> 0.2s

Rumor has it:

• Size is close to 75 MB (with Workshop Tools installed)