What it teaches
Choosing between ch and h. The one rule that never fails is the ending: a word that finishes with this sound finishes with ch.
The second is the swap: ch often turns into sz in a related word — mucha and muszka, ucho and uszy. What is left is a short list of words with h, and a short list is something a child can hold.
How it works
A word with a gap and two choices, the same shape as the other two spelling games. The hint shows the related word with sz in it where one exists.
What to look for
Start with the ending rule alone. It is absolute, it is easy to check, and it settles a good share of the words a child writes in a week.