Hellish Zoo III
Strategy
Takes about 30ish min. Do not buy Summoning duration upgrades.
Keep casting Unclean Knowledge -> Fire Ball until a summoning spell becomes available then cast it after UK. Then keep repeating the pattern.
This challenge can be sped up by cloud save/loading repeatedly to refresh summon timers.
AFK Version:
1) Set Summon Infernal Thrasher and Summon Horned Incinerator to autocast.
2) Fully charge Unclean Knowledge, Fire Ball, and your summon spells.
3) Autocast Unclean Knowledge and Fire Ball (in that order). As these both have a duration of 6 seconds, they effectively earn the 2x bonus on their own.
This strategy takes approximately 20 minutes.
Attributes
Attributes don't matter much. Don't put more than 24 in Spellcraft. You don't need to extend the summoning spells duration, or it will become tedious.
If playing AFK, max out Wisdom. This is to ensure you earn enough spell shards to keep casting every 6 seconds. Optionally, follow by maxing Spellcraft and then Mastery.