I designed a DST friendly "fire farm" for easy mass farming of Pigs, Bunnymen, and Beefalo.

[Sicko Hog]

Here's the whole thing in a 10 second gif, in case you're impatient or just want to see the design.
Credit to Our Own @Electroely for explaining the logic behind fire damage, this wouldn't have appened without him.

And here's the actual guide! You'll need all of this + a potter's wheel and some bait.

Place down a dominant turf like carpet, if you're worried about aesthetics. The farm will take up all of this turf tile and a bit of space above it.

Throw down 4 stacks of 10 rope in these spots, the fire damage from them will stack to quickly kill all of the mobs inside.

Place 14 non-flammable walls.

Place 4 gates.

Place 2 marble sculptures, any kind will work. These will trick mobs' AI into thinking there's empty space between the two gates, making it easy to trap them inside.

Place down your flingo, a single rope in front of it as a fuse, and some kind of bait behind it. A powdercake is the best choice, as it takes an ungodly amount of time to spoil and will grab the attention of both pigs and bunnymen.
If you want, you can replace some turf with cobblestone to make it easier to trap mobs.

To get mobs inside like this, you'll want to open the front gate and one of the gates in the back, then grab the aggro of your mobs and lead them inside the farm, closing the back gate after you've got out so they run against the marble sculptures forever. After that you'll want to back away and lose their aggro, their attention will then go to the powdercake and you can close the front gates. After that, light your fuse and wait for the farm to do its thing. The mobs should start dropping like flies pretty quickly, and you can turn on the flingo to put out their drops. Then you can just walk in and collect your loot!
You can also leave the pigs inside the farm until a full moon happens, if you want the extra werepig loot.
Maximum capacity is 20.

Bunnymen can be farmed in the same way. You'll want to be a bit quicker with turning on the flingo after they start dying, since bunnymen drops burn to ash much quicker than pigskin.
Maximum capacity is 20.

Beefalo are very similar to the others, but won't go after the powdercake. You'll just have to be quick with closing the gate after you lose their aggro.
Maximum Capacity is somewhere around 10, more can fit inside but things get glitchy pretty quickly.

[fimmatek]

This looks pretty interesting!

I'm not sure tho how you light the ropes inside the pen? The fire supposed to spread over from the wood gates?

[Sicko Hog]

One rope below the flingo can work as a fuse, though you probably could just light the gates if you want.

[GenomeSquirrel]

this needs a movie, i can't understand how you are getting mobs in that thing, and how you escape

[FreyaMaluk]

i think u can simplify with a wall with the statues in the middle... the mobs' AI is a bit dumb..

many creatures don't go around walls to attack u