12935 -> TIZZY (5625) -> OXBOW (2674) -> GRUFF (858) -> MAMMA (195) and I'll let you guess the rest but my next choice left 43 words, and I survived with only 4 words possible. The rules not letting use a letter you know isn't in the target word drastically cuts your choices, your best bet is to use as few unique letters per word as you can, and as uncommon letters as you can, but as all normal words need vowels you'…
This is not entirely correct (or at least it's worded a bit weirdly).
If you know that A goes in a certain place you can still try a word using A more than once. It's only once you know that A does not appear twice (because you tried a word containing A twice, and the second A way gray!) then you can no longer use A twice.
In your case you tried MAMMA which contained 2 As and the second one gave you the information that there's no second A.