Cards that Feign Death triggers for advantage in the current metagame:
Highmane (Effective card text: Summon two 2/2 beasts)
Sylvanas (Effective card text : Steal one of your opponent's minions at random)
Creeper (Effective card text: Summon two 1/1 tokens)
Scientist (Effective card text: Put one random secret from your deck into play)
Webspinner (Effective card text: Place one random beast into your hand)
Cards that are kind of eh if Feign Death triggers:
Golem
Belcher
Cards that are outright bad if Feign Death triggers:
Gnome
---
Turn 1: Undertaker, coin, Webspinner
Turn 2: Mad Scientist
Turn 3: Webspinner + Feign Death
Feign Death reads "Draw two random beast cards and place one random secret from your deck onto the field." This makes it a 3-for-1 on turn 3, and you still managed to play at least one minion each turn.
You have a 4/5, two 1/1s and a 2/2 on the board. The 1/1s and 2/2 will all pay for themselves even if they are killed. Each of your Webspinners now has two chances to draw you a good beast. Your Scientist will pull two secrets out of your deck, meaning you won't have to worry about drawing them when you're hunting for more those Kill Commands, Unleashes etc.
The question I want answered is that if you have the two legendaries to summon Thaddius in play on the board and you pop this, does it summon Thaddius?
EDIT:
Edited this post quite a bit.
My belief is that the card is absurd as it stands and someone will craft a deck to break it. And playing two is even better - imagine that curve above but drawing into a second Feign Death on turn 4 and popping down an egg. A 5/6, a 0/2, two 1/1s, a 2/2, a 4/4, two secrets in play, four beast cards in your hand.