I’m a little confused on why “er” (二, 儿) is represented by “Master Chief” and “House”. In my mind since there’s no initial and no final, there would be no pinyin at all. So far every character being built up makes sense to me except for this.
Am I missing something?
Our pinyin system was made to minimize the number of sound items you have to learn–so that’s the primary motivation behind placing er with “Master Chief” and “House”
The –er final sound is a special one in standard pinyin–it doesn’t pair with any initial sound, so creating a dedicated association for it seemed excessive. the er sound only shows up a few times out of the many characters ahead, too.
Instead of memorizing a new sound item, we can just conveniently place it in this “null” spot of _- + -_
This helps achieve our objective of minimizing the number of sound items you have to learn–it’s just a convenient way to put the special case of er into the system without creating a new sound association. 
I hope that answers your question!
As Phil mentions, that’s a peculiarity of our pinyin system, inherited from the Marilyn Method which our system is based on.
I think it may be worthwhile for us to change things around and introduce an -er final as a further simplification, eliminating this special case. We’ll just need to find a good place association for -er.
Thanks for the explanation @phil !
That sounds like a good idea to me. I feel like that’d make it less confusing for people (like me) that aren’t familiar with the Hanzi Hero documentation.
We will roll out this change this Monday in the next curriculum update, adding a new “-er” final to get rid of this weird special case that doesn’t really make sense.
We chose “arcade” to represent it, since “-er” in pinyin is sort of between “er” and “ar” sounds in English (roughly). Also we couldn’t find any location name that began with “er” in English 
.
Thanks again for the feedback. 