The mouse came there and cut the net. 

Once upon a time there lived a lion in a forest. One day, lion had a heavy meal.

It was sleeping under a tree. 

After a while, there came a mouse and started to play on the lion, so lion got up with anger. The lion started to kill it. The mouse requested the lion to forgive it.  The lion felt pity and left it. 

One day the lion was caught in a net, but the mouse came there and cut it.

I think the creatures  helps each other and lives.

a friend in need is a friend indeed. (2019) English for student.