OK I'm gonna propose that Crawdaunt be added to the threatlist. I think some people, me included, may have nudged at it before but never got a response so I'm gonna try to make a serious pitch.
Crawdaunt has 120 Base Attack, 55 Base Speed, and Dragon Dance. He has two useful STABs that get further boosted by Adaptability which means he can run Waterfall and Crunch without the need to run coverage moves at all (not that he has any worthy of mention).
He can hit 342 Speed after one DD, which outspeeds Base 105s such as Scyther so he more or less has the minimum speed necessary to sweep.
Now that formalities are done, here comes the good part. What makes Crawdaunt a fearsome booster is his power, able to destroy many common Physical walls with his STABs or muscle past them if they have a type advantage. The cherry on top is he provides an extremely valuable team support in being able to laugh in the face of all variants of CM Cresselia (bar gimmick sets running Charge Beam...) which makes him an attractive proposition, allowing you to use your enemy's CM Cresselia to your advantage (such as healing members of the team while it CMs up and then sending in Crawdaunt to set up and force it out, and possibly end the match there and then...) and he can do this every single time.
So... Juicy calcs time! (Jolly 252 Atk Crawdaunt with Life Orb after one Dragon Dance using either Waterfall or Crunch; all enemy sets are +Def Nature 252 HP/252 Def unless otherwise stated):
Claydol: 138.3% - 163%
Slowking: 136% - 160.4%
Rhyperior: 132.7% - 157.6%
Rhydon @Eviolite: 131.4% - 156.5%
Moltres: 129.2% - 152.1%
Dusknoir: 127.9% - 151%
Aggron: 111.6% - 131.4% (252 HP/252 Atk/4 Def; Adamant)
Clefable: 105.1% - 123.9% (252 HP/4 Def/252 Sp.Def; Calm)
Gastrodon: 102.8% - 121.1% (252 HP/4 Def/252 Sp.Def; Calm)
Cresselia: 91.9% - 108.1%
Munchlax @Eviolite: 91.6% - 108% (252 HP/4 Def/252 Sp.Def; Careful)
Gligar @Eviolite: 89.8% - 106.6%
Articuno: 83.3% - 98.4% (252 HP/4 Def/252 Sp.Def; Calm)
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Lickilicky: 78.8% - 92.9% (252 HP/4 Def/252 Sp.Def; Careful)
Quagsire: 65.5% - 77.2%
Blastoise: 64.1% - 75.7%
Umbreon: 54.8% - 65%
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Tangela @Eviolite: 42.5% - 50.3%
As you can see, a lot of the Defensive behemoths in the Threat List are OHKOed after one Dragon Dance, while Cresselia to Articuno are OHKOed after SR. The Pokemon that Crawdaunt fails to OHKO are below the dotted line, and they cannot do anything to him especially if he carries Substitute, allowing you to boost up more or simply KO them on the second attempt.
The only common wall that gives him problems is Tangela who can Giga Drain and shrug off your attack with Regenerator. Another defensive Pokemon who walls Crawdaunt is Poliwrath. That's it.
Keep in mind that all of the above Pokemon are the premier walls in RU. Any Pokemon not investing in HP and Defence are crushed. The fact is, if Crawdaunt comes in and you don't have Tangela or Poliwrath, something is going to die in order for Crawdaunt to be revenged. Switching Crawdaunt in is relatively easy and is not just restricted to Cresselia appearances as his Water Type allows him to fit easily into a F/W/G offensive core.
I'm sure I'm not the only one who considers Crawdaunt to be a major threat and I've been seeing it rise in usage lately (saw a few today) so I definitely think it should be recognised on an RU Threat List.