Win cons:
There are a lot of cards in the deck that can generate value over time, but this is highly dependent on draws. The deck tries to include lot of what I call "light synergies" - cards that are fine on their own, but powerful when combined with other cards. For example:
Rat King has 8 targets it can hit.
Assorted Animals can fetch a lot of cards at once, since we have 20 1-drop targets) that can be fed into a Slyvan Splendor (potentially with a Hamlet too) for a bunch more cards.
Cemetery Rats feed the Wolpertinger, as well as Pillar of Zeiros (however Pillar kind of kills the Wolpertinger so only useful in a pinch). Wormelow Thomp protects the Wolpertinger. However, Cemetery Rats could ruin combo potential if they put Ring of Morrigan, Lady Iseult, or the charge enabler in the cemetery. If this becomes an issue then maybe Pendragon Legacy / Lady of the Lake could help prevent that.
Plague of Frogs / Tadpole Pool plus a Pitchfork can be very deadly.
This deck can peter out if the enemy can defend easily, Sylvan Splendor can help refill the hand. With Sylvan Splendor on the board turn 4 (maybe sac some chump blockers to protect it 1 turn) you can cast Assorted Animals for 5, fetch 5 minions, cast all 5 to a Hamlet for free, and draw 5 more cards.
Rat King
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Assuming you start with it in hand and play it on turn 3, going first, there's 55 cards left in the spell book. If you also didn't start with any ordinary rats in hand (and you should mulligan them) then there's 8 possible targets.
From https://www.statscalculators.com/calculators/probability/hypergeometric-distribution-calculator if we put in:
Population size (N) 55
Success states (K) 8
Number of draws (n) 6
Number of successes x 1
Then we get Px ≥ 1 is 62.96%.
In other words, ~63% change to fetch at least 1 rat. You have about a 20% chance to fetch 2+ and about a 3% chance to fetch 3+.
Of course, the odds go up significantly as the deck gets thinned by subsequent Rat King triggers (Genesis and Deathrite, 2 copies, plus potentially more with Lady Iseult). And the odds go down the more rats you play or put in cemetery from Cemetery Rats, of course. But you can play with the link to model some scenarios.
Assorted Animals should always fetch non-rats if possible unless there's a specific desire for e.g. Sewer Rats because you have Putrid Presence - more targets available for the King, plus the non-rat beasts are generally better anyways.
The reason we play 2 Kelp Cavern is to be able to retrieve non-rats that we put on bottom that we want to draw. So the order you bottom the non-rats with Rat King does matter. It also synergizes with Browse which puts on bottom, and Assorted Animals, Dream Quest, and Highland Falconer can force a shuffle if you don't have Kelp Cavern available and want to restructure that bottom stack.
Browse and Observatory can also be used to scout for the King - if Browse reveals 7 cards and none or just 1 are cats, your odds of hitting a rat with the King go up significantly. Conversely, Observatory can show you that there is a rat in the top 3.
Lastly, this deck might be better off dropping air and being Water/Earth/Fire. There's a lot of good stuff in fire, and air brings the least to the table here - the ravens are nice to stall with, since they have lifelink, the black cat is a nice "bogle", and Highland Falconer is kinda nice for deck thinning. Browse is hard to get the threshold for and Dream Quest is a questionable include as only Tawny can even cast it, plus both are 1 copy uniques anyways. So there's a big argument for dropping air altogether and going fire. This idea is in the Rat King section because fire would let us play Granary Rats as another rat target. With 12 targets, then the same scenario as before - playing King T3 on the play and no other rats in hand - would give a 96/80/51 percent chance of getting 1/2/3 rats, respectively, from a Genesis + Deathrite cycle.
The Cemetery Rats could also be swapped for Granary Rats to make the combo more likely, but also reduces Wolpertinger potential.
Summary:
Needs playtesting to determine if Cemetery Rats are worth the include for their synergies:
Given their downsides:
And would playing fire instead of air be better, given everything mentioned above.