When you arrive in the ice age, you will notice that the ground is icy. As a reptile, you will have difficulty walking on the icy surface.
After jumping up the icy slope, you will find a crystal that states that evolution will become harder from now on. However, there is a chance to become a mammal.
Enter the cave.
Inside, you will find that ground to be much more suitable for movement. When you walk to the right, you will encounter some dinosaur spirits that offer a chance to become a mammal (if you meet the requirements.) The game is still possible regardless of which path you choose.
You can return to this location at any time, should you want to evolve into a the mammalian life form.
To unlock the next region, enter the cave and leave once you hear a conversation.
This cave contains mammals taking refuge from the cold.
There are two routes through the mountain: Above and below.
Ikustegas in this region are worth 15 EVO points each.
Tritops are worth 90 EVO points each.
Hogs are woth 50 EVO points each.
These are small mammals that will try leaping as they attack.
This section has icy platforms that need to be jumped across.
The slippery ice will make it difficult for reptiles to cross, since they also need to defend themselves against the birds nearby.
At the end of either the upper or lower path, you can leave the area to the right.
Head to the south to reach the Land of Survival. WHile your ultimate destination is in the north-west, you can't head there because of an ice door.
The brosasaurus will complain that they have enough trouble surviving. Reptiles can easily defeat them, but unevolved mammals may have to jump over them.
Tyrosaurus are located to the south. They will announce they Yeti is coming, but quickly realize their mistake. This location is similar to the final region in the third chapter.
This region is a hot desert. It is a good region to farm EVO points before challenging the Mammoths, as they give 90 EVO each.
Three penguins waddle around, although there are seals further across the icy area.
There are three Mammoths which you have to fight. They alternate between firing three bubbles, and a charging attack.
The bubbles are extremely difficult to avoid as a reptile. Their best chance is to attack right after the bubbles are launched.
You will learn of a location in the western portion of the Land of Survival. Explore the new location, and you will almost instantly be captured and taken into the fort (although you can exit by jumping off the side.)
The two main enemies on the outside of the fort are spearmen, and mounted riders. While you can collect EVO points on them, they do nor provide healing (and as such, you will need to spend EVO points to heal instead.)
The inside of the fortress is filled with flying swordsmen.
To proceed through the fortress as a land-based creature, take the following route:
You will encounter the bird king. He will fly around, and will used ranged attacks to destroy you. However, he is easily locked down with well timed attacks.
When he is defeated, the fortress will collapse.
In the north-west area, you will find the Hynodon. While the animals provide 100 EVO points, they do not respawn until you leave the region.
In this section, you will encoutner the Yeti. His attack is a simple punch. To defeat him, attack as he starts the jump.
After he is destroyed, the Yeti mother will arrive. She has two attacks - a two handed slap, and a ranged wind attack. Jump over the icy wind to avoid taking damage. To avoid the melee attack, make an attack of your own (with a long neck) just as soon as she starts the jump. Make a second attack (timed to connect almost as soon as she lands) to push her back or jump to get out of the way.
Once the Yeti mother is defeated, a short cutscene appears and the final age begins.