I'm trying to get to Croup Manor for a quest.

About halfway down the narrow causeway I run into a Legendary Assaultron Intruder. Whoooooooo boy is this thing nasty!

I can't sneak past because it has incredibly high perception.

My .50 caliber rounds seem to do little more than scratch the paint. In no time it's right on top of me, pretty much melting my power armor (T-45 Model D) and me inside it.

This thing must be several levels above me (Level 21). What does it take to kill one? It's so fast I don't think I could hit it with a Fat Man.

Try laying some pulse mines.

You should probably back away and go level a while somewhere else, because those things are nasty even when you outlevel them.

Assaultrons in general just go right for my nipbles. Like some sort of crazy dominatrix.

Gauss rifle...charge each shot

When I run into a foe I cannot conventionally overcome even with power armor, I find it useful to build my crit meter, then pull out a Fat Man (as it's dead weight most of the time, I'll have my companion carry it around) and introduce them to a critical mini-nuke. If in the very least, you can take out the robot's legs, it'll become much easier to deal with.

Mines. Big help in the fort quest. Not just pulse mines, but any and all mines. Use everything you got. Set the mines, trigger bot, RUN! Then finish it off.

Better yet, set mines, use Fatman, watch it run to its doom as you blast it. I remember giving Sarge a Fatman to the face. Fun times. Actually, I gave him 3.

keep popping the psychojet, backing away, fireing, popping more psychojet. Even level 50+ with a lovely Gauss or Fatman, it's still the only way I can beat those things. Nasty nasty