Get every word into a freestyle.
Study the list, then it disappears and you rap with them. Past four words this stops being memory and becomes a technique — pick one and find out which one your head actually uses.
Glue the words together by sound — each one rhyming or half-rhyming with the next. This is the rapper's own memory trick, and the reason an MC should beat a non-rapper at this. Same words, three encodings — run the same size with a different one and compare the score, which is the only honest way to find out which your head uses.
Where this comes fromThe four-item limit and the value of chunking are general memory research; freestyle word-list recall is not a studied technique, so nothing here claims to measure your rapping. What the app actually adds is arithmetic and scheduling: which words you came back for, and when they are due again.