Source at http://www.gamerhome.net/bbs/viewthread.php?tid=304804
Theory (rewards, number of monsters, and minimum requirement)
Imp Cache【跳跳宝屋】HP4、SPD5/7
Necessary condition: kill one stack with two fire walls, two fire walls Troop configuration: 1
100 Imps 2 Mercury + 1000 Gold horde + lots or throng Single firewall damage needed 40=【Mid Fire 0P/High Fire 0P】=[Mid Fire 2P/High Fire 0P]
150 Imps 3 Mercury + 1500 Gold throng + lots or throng Single firewall damage needed 60=【Mid Fire 1P/High Fire 0P】=[Mid Fire 4P/High Fire 1P]
200 Imps 4 Mercury + 2000 Gold throng + lots or throng Single firewall damage needed 80=【Mid Fire 2P/High Fire 0P】=[Mid Fire 6P/High Fire 3P]
300 Imps 6 Mercury + 3000 Gold throng +horde or swarm Single firewall damage needed 120=【Mid Fire 4P/High Fire 1P】=[Mid Fire 10P/High Fire 7P]

Naga Bank【那加银行】HP110、SPD5/7
Necessary condition: kill one stack with three fire walls, two fire walls Troop configuration: 1-1-1-1-1-1-1
10 Naga 8 Sulfur + 4000 Gold several+few or pack Single firewall damage needed 74=【Mid Fire 2P/High Fire 1P】=[Mid Fire 6P/High Fire 3P]
15 Naga 12 Sulfur + 6000 Gold pack+few or pack Single firewall damage needed 110=【Mid Fire 4P/High Fire 1P】=[Mid Fire 9P/High Fire 6P]
20 Naga 16 Sulfur + 8000 Gold pack+few or lots Single firewall damage needed 147=【Mid Fire 6P/High Fire 3P】=[Mid Fire 13P/High Fire 10P]
30 Naga 24 Sulfur + 12000 Gold lots+several or lots Single firewall damage needed 220=【Mid Fire 9P/High Fire 6P】=[Mid Fire 20P/High Fire 17P]

Medusa Stores【美杜莎宝屋】HP25/30、SPD5/6
Necessary condition: kill one stack with one fire wall, three fire walls Troop configuration: 1-1-1-1-1-2-2
20 Medusa 5 Sulfur + 2000 Gold pack+few or lots Single firewall damage needed 100=【Mid Fire 3P/High Fire 0P】=[Mid Fire 8P/High Fire 5P]
30 Medusa 6 Sulfur + 3000 Gold lots+several or lots Single firewall damage needed 150=【Mid Fire 6P/High Fire 3P】=[Mid Fire 13P/High Fire 10P]
40 Medusa 8 Sulfur + 4000 Gold lots+several or lots Single firewall damage needed 200=【Mid Fire 8P/High Fire 5P】=[Mid Fire 18P/High Fire 15P]
50 Medusa 10 Sulfur + 5000 Gold lots+pack or horde Single firewall damage needed 250=【Mid Fire 11P/High Fire 8P】=[Mid Fire 23P/High Fire 20P]

Dwarven Treasury【矮人宝屋】HP20、SPD3/5
Necessary condition: kill one stack with two fire walls, three fire walls Troop configuration: 1
50 Dwarves 2 Crystal + 2500 Gold lots+ a pack or horde Single firewall damage needed 100=【Mid Fire 3P/High Fire 0P】=[Mid Fire 8P/High Fire 5P]
75 Dwarves 3 Crystal + 4000 Gold horde+ a pack or horde Single firewall damage needed 150=【Mid Fire 6P/High Fire 3P】=[Mid Fire 13P/High Fire 10P]
100 Dwarves 5 Crystal + 5000 Gold horde + lots or throng Single firewall damage needed 200=【Mid Fire 8P/High Fire 5P】=[Mid Fire 18P/High Fire 15P]
150 Dwarves 10 Crystal + 7500 Gold throng + lots or throng Single firewall damage needed 300=【Mid Fire 13P/High Fire 10P】=[Mid Fire 28P/High Fire 25P]

Dragon Fly Hive【龙蝇树】HP20、SPD13
Necessary condition: kill one stack with one fire wall, one fire wall Troop configuration: 1-1-1-1-1-1-1
30 Dragon Flies 4 Wyverns lots Single firewall damage needed 120=【Mid Fire 4P/High Fire 1P】=[Mid Fire 10P/High Fire 7P]
45 Dragon Flies 6 Wyverns lots Single firewall damage needed 180=【Mid Fire 7P/High Fire 4P】=[Mid Fire 16P/High Fire 13P]
60 Dragon Flies 8 Wyverns horde Single firewall damage needed 240=【Mid Fire 10P/High Fire 7P】=[Mid Fire 22P/High Fire 19P]
90 Dragon Flies 12 Wyverns horde Single firewall damage needed 360=【Mid Fire 16P/High Fire 13P】=[Mid Fire 34P/High Fire 31P]

Griffin Conservatory【狮鹫宝屋】HP25、SPD6/9
Necessary condition: kill one stack with two fire walls, four fire walls Troop configuration: 1
50 Griffins 1 Angel lots+pack or horde Single firewall damage needed 125=【Mid Fire 5P/High Fire 2P】=[Mid Fire 11P/High Fire 8P]
100 Griffins 2 Angels horde+lots or throng Single firewall damage needed 250=【Mid Fire 11P/High Fire 8P】=[Mid Fire 23P/High Fire 20P]
150 Griffins 3 Angels throng+ lots or throng Single firewall damage needed 375=【Mid Fire 17P/High Fire 14P】=[Mid Fire 36P/High Fire 33P]
200 Griffins 4 Angels throng +lots or throng Single firewall damage needed 500=【Mid Fire 23P/High Fire 20P】=[Mid Fire 48P/High Fire 45P]

Cyclops Stockpile【独眼宝屋】HP70、SPD6/8
Necessary condition: kill one stack with one fire wall, two fire walls Troop configuration: 1-1-1-1-3-2-2
20 Cyclops Each resource 4 a pack +a few or lots Single firewall damage needed 280=【Mid Fire 12P/High Fire 9P】=[Mid Fire 26P/High Fire 23P]
30 Cyclops Each resource 6 lots +several or lots Single firewall damage needed 420=【Mid Fire 19P/High Fire 16P】=[Mid Fire 40P/High Fire 37P]
40 Cyclops Each resource 8 lots + several or Lots Single firewall damage needed 560=【Mid Fire 26P/High Fire 23P】=[Mid Fire 54P/High Fire 51P]
50 Cyclops Each resource 10 lots +a pack or horde Single firewall damage needed 700=【Mid Fire 33P/High Fire 30P】=[Mid Fire 68P/High Fire 65P]