Multiverses

Multiverses 1
"You can only unlock 2 of the following: Theory, Hadronic Challenge, Quantum Foam and Skyrmions (unlock them by opening their tab)."

Normal Stadium Challenge completions are also reset.

Rewards
Normal Stadium Challenge rewards are much stronger, but their challenge goals are much higher. Distance boosts Skyrmions gain.

Multiverses 2
"Maximum Velocity is forced to be active, Pion & Spinor Fields are 40% weaker, and Time Speed & Maximum Velocity are brought to the 1.3th root."

Rewards
Every third Derivative Boost gives you an extra Derivative shift (maxes at 6 shifts)

Multiverses 3
"You can only unlock 1 of the following: Ascension, Stadium, Pantheon and Derivatives (unlock them by opening their tab). Quark & Lepton exponents are set to 0, and Entropy is disabled."

Rewards
There are 5 new Dark Expender

Multiverses 4
"You are always trapped in the Theoriverse at Depth 4.5(unaffected by any depth reduction), which also affects Pion & Spinor gain."

Rewards
Unlock 3 new Strings

Multiverses 5
Time speed is brought to the 3.6th root.

Rewards
The Purge Power effect goes below zero, and unlock Phantoms (a new Pantheon section). Heavenly Chip & Demonic Soul effects are much stronger.

P.S. There is no guide to each multiverse.