This is rather strange sounding creature. We are often able to look at a trait and identify what it is for (even if not able to identify how it evolved). Example: We can look at a cheetah and see how it's skeletal structure enables it to move so quickly. I'm trying to imagine why a creature would have big floppy ears, tentacles, fur, and be so large. Consider the big ears. Animals with large ears often use them for thermoregulation (think elephants, rabbits, and the fennec fox). If the tentacles are for locomotion, how would it have evolved them and why? Hmmmmm... [Scratches head] And fur? The major sea mammals are the cetaceans (dolphins and whales). They've swapped their fur for blubber as insulation. Much more effective in the water.
Now. How realistic do you want this creature to be? The more plausible you want it , the more I would think that you would consider how it evolved. I can't really see any cephalopod developing ears and fur (and the physiology that accompanies those traits). As mammals however we (I'm assuming you're not a cephalopod) have shown that we are quite capable of adapting to many different environments. Endothermy! (Warm-bloodedness). Ok. So we've got some sort of aquatic mammal. If it lives right by the water I'm not sure why he's got bunny ears. He (or she) can keep cool with the water (If they can't keep cool with the water because it's too hot then they're probably already f*cked). I guess if they were to continue spending a significant amount of time outside of the water and it was really hot then it could be advantageous for your hexabunny (ew...) to maintain the trait of large ears. Large ear size would serve no advantage in the water as far as hearing goes but it could still be useful on land.
This brings me to the point that any organism is going to evolve to be best suited to their particular habitat. So you're also going to want to spend a lot of time thinking about their environment. So if the big ears are for thermoregulation then I'm thinking this hexabunny is spending a lot of time in the heat away from water. But it's also got tentacles so it's spent a hella lot of time in the water too... 671
Hmmmm... Maybe it migrates? Maybe your hexabunny was just a regular bunny that evolved to take advantage of the food source on the other side of the giant wetland (let's say its a huge wetland but not too deep). The bunny used to to traverse it only when it was dried out but a few hexabunnies were able to do so when it was slightly wet and were able to outcompete their hydrophobic counterparts. As the climate continues to change the wetland gets bigger and bigger and the hexabunny (not really a hexabunny yet. Kinda lacking the six tentacles part right now. Six?) is able to continue adapting to the increasing amount of water . So this food must be really good. What is it? Not sure. But it's hella worth it apparently. So now you've got an aquatic bunny. Why does it continue to deal with the heat on land? Ummm... Let's say that the seasons are really drastic and in summer where the hexabunny lives is really hot and dry. Now why does it have tentacles and how did it get so damn big? I'm imagining that a rabbit would evolve to use those super cool feet more like frog flippers. Really have no idea why a mammal would give up our super cool limbs for tentacles. And the size... Why would it be advantageous to be so large? So as to not be eaten by predators perhaps? Maybe the water's actually really cold (at least where it swims. Maybe in the really deep cold currents?) and it is big because that means less heat loss (greater volume to surface area ratio. See the enotes website). But then why does it still have fur? I guess to help deal with the cold when outside of water. So your hexabunny (which is actually just a big ass aquatic bunny right now) has to deal with some dry hot ass summers, some super cold deep sea diving and also cold on land (Maybe your bunny burned all it's fat while swimming in the cold so that's why it keeps its fur). So this guys doing some serious migrating and dealing with some crazy seasonal changes. That's all I've got for now... Phew. Good luck!
Evolution of cetaceans: https://en.wikipedia.org/wiki/Evolution_of_cetaceans
Migration: http://icouzin.princeton.edu/wp-content/uploads/2013/11/Shaw-2013-The-American-Naturalist.pdf 671