Remove the "Dry Age" and "Ice Age" from the challenges, and make them their own different modes.
These new modes could have new creatures, new bosses, and evolutions exclusive to them. These exclusive evolutions could possibly be unlocked in the base mode by doing certain tasks in the new mode. However, fur and scales should be unbanned, but the modes should be a lot harsher to survive in almost requiring them.
Here are some evolution ideas that could be utilized in these biome modes.
Desert:
Large Ears = +15% Heat Adaptation +20% Senses (Some animals use large ears for heat dissipation. They pump blood into their ears to radiate heat away from their body and into the surrounding air.) Example: Elephants, Fennec Foxes, and Aardvarks
Hump = Hump could be moved and unlockable from the desert mode.
Dig = Dig underground like a Sandshark for 3s-5s, reduces damage by 55% and increases speed while underground. [requires burrow] (A lot of lizards and amphibians dig into the ground to avoid heat.) Example: Spadefoot Toads, Meerkats, Jerboa
Scavenger = Scavenger could be moved and unlockable from the desert mode.
Tundra:
Huddle Together = 10% x (Number of charmed creatures) Cold Adaptation. (Some animals huddle together for warmth) Example: Bees, Penguins, and Mice
Subcutaneous Fat = Subcutaneous Fat could be moved and unlockable from the tundra mode.
Antifreeze Glycoproteins = 50% Cold Adaptation -30% Heat Adaptation. (Some animals have biological antifreeze to survive sub-zero environments.) Example: Snow Flea, Antarctic icefish, Snow Mold
Camouflage = Become undetectable for 3s-5s, Lasts a few seconds longer in desert and tundra biomes. (A lot of animals have white fur to blend in with the snow, and in deserts animals are tan colored for the sand.) Example, Polar Bear, Sidewinder Rattlesnake, Arctic Hare
These modes could introduce new weather to make them more harsh to survive in, like sandstorms, and snowstorms. These could reduce movement and visibility of the player.
There could also be a sandworm final boss for the desert mode, and an ice dragon final boss for the tundra mode.
#Biome Related Suggestion
humble creek
Some new biomes would also be nice
Like marshes and actual beaches