this is a bad advice as the number of cards by themself doesnt say anything about your current situation. its all about the quality of the cards you have. you can have 8 worthless randomly generated Elemental Allies in hand with an empty board and by your logic you shouldnt use Box.
I have actually thought that it is obvious that when I write “Only use box after box is played you have 7 cards left, 6 is better” you have to add in your head, [only if the situation allows it]. I mean it’s obvious that vs a DH you might play it with Dragon Caster and don’t care if you burn double Alex and Zeph, as long as you survive.
It’s just that on average you can expect to draw something/copy in your hand.
Too often I have seen box being played at the wrong time vs Warlock or Priest with 9 or so cards in hand…
It’s actually kind of hard watching a priest having stolen a Puzzle Box use it with a near full hand against a low threat board it’s painful enough watching them burn half a dozen cards… but even more painful when they aren’t punished by the high chance to draw cards and it goes well for them.
BoringBox of Anduin, 10 cost priest spell, Cast a random spell for each time you passed this game.
DumpsterBox of Thrall, 10 cost shaman spell, Cast a random spell for each time you lost a game today.
MurlocBox of Uther, 10 cost paladin spell. Cast a random spell for each murloc you played this game.
You know I actually had one of those Puzzle Boxes today…
Turn 5 coin Dragoncaster Puzzle Box against a moderate DH board… at the end of it all of his minions were still alive (one in fact had gotten buffed), I had one useless secret and burnt half a dozen cards.
The next game was a Spell Druid that I almost certainly would have won against if Puzzle Box didn’t cast Shadow Council (got my Reno, which is a critical card for the matchup).
Sometimes this game makes me sad.