Mulligans
General Mulligans
Generally, just mullaganing for stealth minions and efficient draw just allows you to push the game forward into good tempo plays. Don't go for greedy plays and just aim to play on curve and hit face. The general mulligan is good against all archetypes with only slight variations depending on how fast you need to be to stay ahead.
Aggro Mulligans
While the general mulligan still holds up, aiming to get SI:7 Agent and Wicked Stab to help fight for the board are solid options primarily against hyper-aggressive decks. Weapons also assist in this fashion, while not as successfully as you still don't want to take much damage against these decks.Midrange Mulligans
In a midrange matchup, the game plan barely changes at all. Just playing on curve should net enough tempo and damage to win. You should be generally faster than these decks, pushing more early damage with stealth minions and using burn to hit early lethals.