Scratch Link: Location (Heihei is dragged around and the Kupu changes with its location).
Lyndsay Head: Making Māori Sentences is a great reference for levels 1 to 4. Ray Harlow's Book, A Māori Reference Grammar covers level 1 through to 8.
Exploring the Grammar of Te Reo Māori has helped me learn what the sentences actually mean. Also, seeing the patterns helps me retain the new knowledge.