Widdershins

Are you sure you didn't call me in as a dual-type adviser too? 

I can confirm all of this science, though. Antifreeze-blooded fish are definitely a thing that exists. Apparently polar bear livers are extremely toxic, too, due to ludicrous amounts of Vitamin A in them causing a very unpleasant and self-explanatory affliction called 'hypervitaminosis A' if eaten. Rather similar to carbon monoxide poisoning in terms of symptoms, and involves plenty of peeling flesh, but I'm not sure how it would lend itself to poison-type attacks.

 Hmm... Well.... issue with an aquatic snake...

 I know the franchise, if anything comes even near the water, it gets water typing slapped right on it! We're already fairly drenched in Water/Poison types... but a water snake would be pretty cool too! Could always use Dhelmise's screwball logic that the Water just happens to be where its found and the pokemon could just as easily maneuver on land. Which... beats me why we're capable of taking all the fish pokemon out for battles on land, but... I digress...

 Tentacruel isn't directly a one-to-one translation, but Malamar is clearly squid & Octillery is clearly also derived from Octopi. Plenty of room there for finagling! ...though I might be a bit bias in having more cute tentacles around!

 That's sorta the crux there though. It's important to point out both Poison & Ice as more integral to the creature rather than its method of locomotion. Heck, I'm surprised they didn't try to slap on a Flying typing onto Inkay!

 Hmm... that's an idea... but I'm not sure how feasible attaching crystal to a viscous-form goobody. Alolan Muk has its embedded pebbles and there's now Melmetal... but those appear to be a seperate foreign object lodged in the materia...This'll have to be more a topic for Duality, more experience on gooeyness from thy.

 And of course, You'd be a "Math/Science Type Advisor Pokemon!"

Hmm. But its not actually literal Antifreeze? Like, you can't just wring the fish out over your engine block? ...there's a mental image for you...

 ...but this goes back to my prior topic. There's a bit of half logic to follow with Pokemon. Something like the Pokedex saying that "This creature developed its toxic blood to live in colder climates, and has since used this quality to make itself disgustingly toxic to any would-be predators." But I feel implied that we'd have to somehow weaponize the toxic blood to have it qualify as a Poison.... typing...

OMG! Arctic Horny Toad! You think Game Freak would go for a pokemon that literally squirts its blood out at its opponents in battle?!!? 

They say that there's only two true arrangements of matter: crystalline and viscous. Anything that one might call 'solid' that doesn't have a rigid crystalline arrangement of molecules is in fact viscous - just with very high viscosity. Hence, integrated transitions from true crystals to viscous material aren't chemically feasible. Not all ice is true crystal, admittedly, but even so you'd be hard-pressed to form any sort of graduated phasing from ice to gloop. Generally, also, with ectoplasmic entities, their outer membrane must be kept almost entirely intact at all times for them not to leak out their innards, so they'd have to surround the chunks of ice embedded in their surface with membrane underneath and around, as foreign objects.

The question, then, clearly, is why they'd carry around chunks of ice held gingerly in their outer membrane. In answer, I propose 1) for the purpose of being a readily available source of water, since ectoplasms contain a lot of water and thus would need replenishment regularly if on land due to dehydration/evaporation, and 2) for the purpose of temperature regulation, since ectoplasms can't just 'pump blood through veins near the surface' like us mammals do and thus would probably benefit from objects constantly on hand to sink excess heat into. If it produced enough heat to need any significant quantity of ice for this reason, though, it would strongly imply that its metabolism is very high and therefore that it would need a lot of food to maintain its energy. Much glomping would be required, in short.

I think it is actually antifreeze of a similar nature to what we put in car engines. Something like ammonia, maybe? I could be wrong, though.

I very much like the Arctic horny toad idea. Those amphibians are terrifyingly great.