Two things from classic than seem to not work on Warmane (Onyxia at least)

1. 2X poison roll MH 1x poison roll OH on mutilate
this bug caused for mutilate to be able to double procc poisons on the main hand, which turned out to be a huge dps increase for rogues by itself, and you could take it a bit further by putting your fast weapon+deadly poison on your main hand, for you to have more instant poisons proccs in exchange of some mutilate damage, on a 1h sample size i never got a double MH proc from a single mutilate, fast weapon in the mainhand seems to be a dps decrease on Warmane Onyxia, and assassination rogues overall do less damage than they should
2. Roll of poison/trinket on Feint
This is pretty self explanatory, the spell feint had a roll por poisons/trinkets on classic, which made glyph of feint a marginal dps increase if you just cast it, this isnt as meaningful as the first one but its a difference i noticed.