Infernal Crops
Short to Medium Length Challenge - 30 Minutes ~ 2 Hours - Depends on leveling up.
Strategy
Use the Daemon, or any other strategy, to get experience up to Reap What You Sow (level 81). When you have the spell, change to the Spellhound, set Fire Ball, Summon Infernal Thrasher, Unclean Knowledge and Hellrage to reckless autocast and you should quickly get to level 140 (with the Tier I pet) in order to complete the challenge. Reap What You Sow is dependent on Total EXP, not how much you need to get to the next level. Finishing at 140 instead of 153 saves much more time than is predicted.
Attributes: Spellcraft 100, Mastery 50
Also fairly easy with Geode, Hellstorm, Unclean Knowledge and a maxed Spellcraft.
Notes
You can also use the Pit Lord for this challenge in order to receive a secret achievement. Be advised that Tier II pets have different experience progression; you'll need to level them to 115.
If you can get to Hellstorm in a short amount of time, use Interrogator instead, as Hellstorm's experience scales with evocation efficiency.