(It is unlikely that I would ever keep 2 of either of these cards in my opener. Potentially the spellstone if you are expecting a control deck)
Do Not Keep:
1) Omega Defender - You're going to be waiting a long time to play this card lol.
Generic 8 Mana Combo:
1) Play Valeera the Hollow.
2) Play Omega Defender
3) You will then want to add as many Omega Defender to your deck with your Lab Recruiters as possible so that you increase the odds you keep drawing into Omega Defender, while still maintaining the board presence you need to win the game. As well as ensuring you always have 1x Lab Recruiter left in the deck.
You may have noticed the deck list has only 1x Omega Defender, which is because I am mainly trying to increase the odds that Roll the Bones will draw more than 1. You also generally don't want to use it until the end of the game anyway.
So why 2x Lab Recruiter?
Forcing End Game:
There is still the issue that your deck still has a lot of cards in it meaning the odds of drawing your copied Omega Defender will be around 3/13 to 3/16, by the time you reach turn 11+ with all your draw power.
Preparation + Myra's Unstable Element allows you to purge the remainder of your deck for 2 mana, and then trigger the Generic 8 Mana Combo meaning you now have 3x Omega Defender and 3x Lab Recruiter left in the deck.
(This does however create an argument for having a 2nd Omega Defender)
Card Choice Discussion:
1) Roll the Bones - It has been working as an alright turn filler card and I haven't felt a great loss in tempo, but it almost always draws me only 1 card. Even when it does that I haven't felt horrible about it.
But this is probably the first card I would cut and I would potentially replace it with Elven Minstrel to keep draw speed high, but we aren't running many good combo starters. Generally I like to couple him with Fire Fly.
2) Pogo-Hopper - This is similar to Omega Defender but it obviously runs a lot slower early on and requires a lot of draw power to really get presence on the board. It also does not feel great wanting to hold on to such a small minion to ensure it gets added to the deck. The same reason why I opted to cut Omega Defender.
3) Heals: Zilliax and Rotten Applebaum - These are your only heals, I had been running Plated Beetle, but I felt they were losing me draw power / tempo, when I could just use a throw away Lab Recruiter if necessary.
(You almost certainly want to play the Lab Recruiter on an empty board so you don't add more useless cards to draw, before you empty the deck.)
If you wanted to be more aggressive you could potentially use Hench-Clan Thug.
4) Sonya Shadowdancer - You really want to abuse her power with the Blightnozzle Crawler's Radioactive Ooze, getting more Loot Hoarders or Kaboom Bots are fairly good as well. Otherwise she could be replaced, but is a fairly mana cheap medium risk tech card.
(Keep in mind you want to be able to play out your hand so you can keep drawing more cards and / or your entire deck. Myra's Unstable Element)
5) Necrium Blade - Everybody likes to destroy / replace this weapon so be mindful of that. If you really need it to trigger you can always weapon up with your hero power and break it yourself to trigger an extra deathrattle.
Against aggro decks I'll also trigger it on Rotten Applebaum.
6) Lesser Onyx Spellstone - With more aggressive deathrattle cards I have been feeling good about the usefulness of this card, I weigh it a bit more than Vanish and Sap, but I essentially use them all as silence.
Make sure to be mindful of the counter for deathrattles played if you have 2 of the card in your hand so you do not throw the one closer to gaining the next upgrade.
Additionally during the end game I try to be aware of the counter and try to use Shadow Reflection on cheap deathrattles to increase the card's counter.