When Fungus Breeder is killed, it gives 25 gold and spawns 2 Munchshrooms.
Those 2 Munchshrooms give 24(2x12) gold when killed and spawn 2 Boomshrooms each.
Those 4 Boomshrooms give 24(4x6) gold when killed.
The wiki is wrong about this. http://kingdomrushtd.wikia.com/wiki/Gold
All in all, 25+24+24=73 gold can be earned from one Fungus Breeder.
https://youtu.be/S3B0tHklp3o?t=9m48s
But when polymorphed or instantly killed, it doesn't spawn anything and gives only 25 gold.
2 Boomshrooms spawned by the dead Munchshroom give 12(2x6) gold when killed.
Fyi,
Poukai Rider: The Rider gives 25 gold when killed + the riderless Poukai gives 15 gold when killed = 40 gold
Worg Rider: The black Worg gives 25 gold when killed + the unmounted Orc Champion gives 25 gold when killed = 50 gold (Death Ray, Oni, Hacksaw cannot insta-kill both of them but only the Worg. When Worg Rider is polymorphed and then killed (other than being clicked to death), just 25 gold is given.)
Giant Wasp Queen: The Queen itself gives 40 gold when killed + 6 Giant Wasps that are spawned after death give 48 gold when killed = 88 gold
Mounted Avenger: The beetle gives 60 gold when killed + the dismounted Twilight Avenger gives 30 gold when killed = 90 gold (when insta-killed while riding a beetle, only 60 gold is earned. https://youtu.be/-TSURgIR1uc?t=8m12s)
(and... Boomshroom that is transformed into Munchshroom by Fungus Breeder also gives 12 gold when killed. and 2 Boomshrooms that are spawned after death give gold, too.)