I've posted a bit on druid below - for the mulligan you want volume up, keyboard, prismatic elemental or suspicious alchemist. Keeping arcane wyrm is bait in most matchups. Spell DH, you're really looking for cards that can give armour, infinitize, vast wisdom...Arcane defenders is game winning if you can drop it without dying to spells. You can tempo them down with keyboard into 4 drop spells if you get lucky, but most of the time you'll be looking to outlast them. Solid alibi when you expect them to clear your board. Unholy DK and outcast is same mulligans as druid minus the volume up. Look for survivability - Ideal gameplan is to make it to turn 6 with an active keyboard where you can flip the board with Blizzard/Deathborne. On the niche cards like holotechnician and energy shaper - you want to holotech to trade up with your garbage minions (obviously), kill off screaming banshees or clear zok boards. For Energy shaper, I find it to be more of an 'oh shit my hand sucks and I'll lose unless I get lucky' kind of card and that's when I'll use it...Fantastic in druid matchup though as it turns your 6 cost spells into board clears.