The Mouse is one of the simplest and smallest animals in the game - only freshly-upgraded Rabbits and/or Trout and Arctic Hares are slightly smaller. Along with the Shrimp, Rabbit, its Arctic and Ocean equivalents, and Crab, it is the only animal without a Tail. Its base is gray and features a gray triangular snout with a grey-pink circular nose, large black eyes, darker gray ears, and a pink tail. The eyes are bigger than most animals, implying a small defenseless animal, and possibly for others to take pity on it. It didn't really work.
The first thing you'll want to do is to find a Berry Bush, as this will be your quickest method of getting to Rabbit. If you can find a full Berry Bush, your time as Mouse will only be a few seconds at most. As an added benefit, finding a Berry Bush that has a Hiding Hole in its proximity will allow quick escapes from swarming predators.
Always be on the watch for Rabbits, Pigs, Moles, and Deer. Be wary when getting close to a Hiding Hole, as smart predators might be lying in wait, though this goes for ''all'' animals and not just mice.
Fortunately, higher-ranked predators such as Moles and Deer probably won't eat you since they consider it a waste of time to chase after mice as they give relatively low experience points.
Healing Stones are a great way to level up as they can easily fill up experience bars of lower-ranked animals such as mice and Rabbits. While Healing Stones can restore your health, you are still vulnerable to attacks and death, and so, be wary of predators while leveling up via Healing Stones.
When running from predators, use your small size to your advantage and squeeze through narrow gaps. This can be especially useful against Pigs and Deer, but you may have to take a few hits before squeezing through certain holes. Rabbits can squeeze through many of the spaces that you can, and Moles can burrow underneath. Be careful on Mud as both Pigs, and burrowing Moles are faster than you. There are also Deer that may visit a patch of Mud to dig for food, and may or may not eat you.