Here is the list of potential minions you can get.

If you're playing a class that has a 3-Cost minion; it will be exculded from the potential set.

The 3-Cost minions are pretty interesting to me since they a lot of diverse effects. Ranging from Mech synergy to being great with spells.

Here's a tier that is probably inaccurate but oh well...

Tier 1: Probably always great.

• Edwin VanCleef - Every deck has cards in it, so it's not unreasonable to assume you can get a pretty powerful VanCleef.
• Aldor Peacekeeper - Reducing an enemy minion's attack is pretty nice.
• SI:7 Agent - Dealing 2 damage is also pretty neat.

Tier 2: Good but not great.

• Dark Cultist - Not really a threating body to play after a 5 Mana minion. Plus it does nothing the turn it's played.
• Druid of the Flame - Similar to Dark Cultist.
• Flamewaker - Can affect the enemy board, if you can combo it with spells.

Tier 3: Average and probably nothing special.

• Soot Spewer - Great if you're running a spell heavy non-Mage deck. But probably just a 3/3 mech for 3 Mana most of the time.
• Metaltooth Leaper - Similar to Soot Spewer, a bit more powerful in Mech decks.
• Kirin Tor Mage - 4/3 for 3 most of time. Unlikely to have secret synergy since you won't get it if you're a Mage.
• Scarlet Purifier - Sure it kill off enemy minions with Deathrattle, but it can also deal damage to your minions.
• Grove Tender - Card draw/Ramp for you and your opponent!
• Iron Sensei - Worst of Tier 3 since it has -1/-1 in stats. Really shines in a Mech deck though.