Butcher
Nothing much is new here. An Ironman team can’t afford to take on the Butcher directly. Use one of the two common methods:

Grated room - Find and clear out a grated room making sure not to kill any monsters at the door or else it will be blocked. The warrior lures the Butcher while the others wait inside the room. The warrior then run back through the door and close it before the Butcher can enter. You may want to have another teammate standing by the door and close it when the warrior gets through. Shoot with all available bows. This tactic is quite dangerous; if it fails the whole party may become fresh meat.

Stair trap - Before the rogue uses the stair trap, the remaining party should go into a room far off the path from the Butcher to the stair-down, or go up to lvl 1, or down to lvl 3. This is necessary to avoid the Butcher from being sidetracked due to desync. The rogue then lures the Butcher to the stair-down and circles the stair tightly until Butch is stuck in the stairway. Don’t forget to check and get the bow repaired first.

See also:
TPKill method in the Town Portal section, for the best way to kill the Butcher.

King Leoric
Advance slowly when in dlvl 3, you may run into Leo at anytime. If the team is lucky enough to find Leo with a few rooms already cleared, it is best to run away and find alternate routes to clear the level as much as possible to gain more exp, and perhaps find a Holy Bolt spell book/staff. Agree on a course of retreat when someone types “Leo” - else the team may get split up. Never run back to the stair-up!

Try to isolate Leo and face him alone. Use hit and run tactic if he is surrounded/followed by his helpers - Spread the horde by running and then killing some when Leo is at a distant. Still, the best tactic is to retreat to a defendable door and set battle formation. Don’t forget to switch to blunt weapons for more damage.

Use the Mage Shotgun formation when the team lacks Holy Bolt. This is the first of many reasons why I am an advocate for rogue as shield/host. In an average Ironman game, the rogue can easily have 60+ Dex if she puts all lvlup points to Dex. She can block Leo quite well and will last a long time with minimal potion consumption. The rogue has enough tohit to get in a few swings in between blocking while the warrior deals out most of the damages without wasting time on blocking and recovery. The mage, of course, may use offensive spells for support as well as casting Heal Other on the “Shield”

Leo is as good as dead if you have Holy Bolt. The formation below is another alternative when playing traditional style (warrior as host/shield and bow-only rogue), and the mage knows Holy Bolt. Note that Leo is allowed to step into the room one pace so that the rogue has a straight shot at him. Another strayed arrow avoided is another potion saved.

See Also: Charis' Guide to Melee vs Leo