After accuired passive deathrattle triggered twice, every deathrattle could be triggered 6 times in total.

Got lucky by using Hunter, combination as follow
Anomaly Mode: Nesting: After a minion is played by either player, it gains “Deathrattle: Summon a 1/1 copy of this minion.”
Passive 1: All deathrattle triggered twice
Passive 2: Minions has rush
Hero Power： Pet Training
Start with Tech and Death pack
The key is for any deathrattle, most likely multiplied by 3 times.