Boss: Dark Wisp (no DLC)

Success may vary depending what you draw with Bloomsprite, Ruunin's Presence and Spellwhirl.

Tactics:
Start building neutral lands to give yourself time to react.
If it plays Crystal Dragon in the first 2 turns you might aswell restart.

Boss will drain life off your Orb - ideally save Hold The Line! until you need the healing.
Mind it has 3 Rebel Slingers in the deck (2 damage to Orb each).

Frogify is obviously great to counter Sharra or Radiance.
Preferably use the Emperor's Command/Humbling Vision on the King's Faithful.
Plague Bearer are most efficient early game when it has multiple units out.

Dark Wisp's deck looks somewhat like this:
3x Cutthroat Bandit
3x Freedom Fighter
3x Hunted Outlaw
3x King's Faithful
3x Maceman
2x Master Swordsman
3x Queen's Assassin
3x Rebel Slinger
3x Steamforge Enforcer
1x Crystal Dragon
1x Doom Scythe (the only removal in it's deck)
1x Radiance, Imperial Airship
1x Sharra, Dragonslayer