There are a couple of different species of mammoths added, but what is true about all of them is that they are giant and hairy.
The oceans will become unsafe to visit too - being inhabited by the giant carnivorous, that can eat you up as a whole.
Cenozoic Craft is a great addon about ancient animals the has content to explore.
How to install addons:
- Download addon straight from your device
- Find and open .mcpack or .mcworld files that you download earlier
- Click it to import into Minecraft Pocket Edition
- Open the game
- Create a new world or edit an existing world
- Scroll down to Add-ons section and select the ones you want to apply
- Make sure to enable "Experimental Gameplay"