Okay, I tried this on megamek vs the bot. No human opponents around to play, and I know you can do online megamek, but I am not an online gamer. I took the Exterminator.
Result: Major Attacker Victory
Damn, this thing plays like a Clan mech. So I modified the scenario just a little bit. My version of megamek doesn't have Fist Fire as an option. I also forgot to turn off Forced Withdrawal, not that it really mattered much. I didn't bump up the BV of the command lance all the way to 6000 (forgot to do that too).
Exterminator 4D with a 2/3 pilot, I took Jumping Jack and Melee Master (2 attacks per physical). I think Melee Master actually has a prerequisite that I didn't take, but it doesn't really matter because I only got in like one round of physical attacks (two kicks to the Thunderbolt, hitting each leg and doing only armor). I have Quirks active by default, and my opponents ended up with a +1 bonus to Init the entire time, so I had a hard time winning Init. I also had Extreme Range turned on. Regular LRM ammo because my megamek won't do Thunder ammo.
Defenders had the following: Archer 2R, Thunderbolt 5S, Centurion 9A, Hunchback 4G. All with 4/5 pilots. BV was 2521 (me) to 4798 (them).
I used a 2x2 set of maps. Upper left corner was Countryside 2 (with the twin lakes), upper right was Rolling Hills 1, lower left was Scattered Woods, lower right was Countryside 1 (with the two little lakes). I started on the north edge, they started on the south.
Victory on round 67. Every enemy mech destroyed. The Executioner is down one jump jet, and I am completely out of missiles. AMS never had to fire. Left leg is completely stripped, only 3 IS left. I hopped around most of the game with it wide open, but I kept the to-hits at 10+ for the bad guys and because of Jumping Jack and a better pilot, I needed like 6s and 7s to hit them. Otherwise I was pretty fresh on armor, just some scattered damage but nothing internal.
Attacking from the rear didn't help me at all, the bot was smart enough to keep everybody together. That Hunchback was effectively guarding everybody's back. I had to jump around hills a lot, tried to keep to woods as well, and minimized LOS as much as I could. The extreme mobility allowed me to engage when and where I wanted. 6/9/6 is awesome when everyone else is 4/6. About every 4 or 5 rounds, I'd hit with all 4 mediums (or 3 mediums and the LRM when I still had ammo) and force a piloting skill check. They usually made it, but when they'd fail that's free damage.
I had one really bad round where I was stupid. For some reason I thought I'd won initiative, and went stationary when I had no line of sight. Then the Thunderbolt ran right up adjacent and I was like "oh yeah, they haven't moved yet". He hit with nearly everything and that's when he went internal on my leg. Fortunately all I lost was the jump jet and my sense of safety.
The T-Bolt was the first to drop. I'd scattered some damage on the Archer and the Centurion, but then the T-Bolt moved to nail me when I was stationary. I made it away and managed to slowly strip his armor while the other mechs moved around hills and through woods. Eventually I blew off his arms, damaged his hip, and just slowly picked him to pieces. Lots of keeping no sight to his allies and shooting at him on 6s and 7s. Eventually he was down to two medium lasers and I blew off his leg and put a gyro hit on him. He fell, and then he ejected. That's when I remembered I was supposed to turn off Forced Withdrawal.
I thought about fleeing there. I didn't know if I got the commander (I forgot to check that at the end of each round), but thought some of the other mechs were injured enough, I might be able to get one more.
The Centurion went next. I got chased around all four mapsheets by the remaining mechs, but particularly the Archer and Hunchback (Centurion could never get good sight). 2 LRM-20s and an AC-20 are a nasty combo to fight. Eventually I had a round where only the Centurion had LOS, and I lit him up. Got him in the ammo bin, and he exploded. During this time I got the Archer in the ammo as well, but the bin was empty. What a jerk.
Thought about fleeing again, but I was getting cocky.
A bunch more turns while I slowly whittled down the Archer and the Hunchback. The Hunchie still had a lot of ammo for the AC-20, and I was giving him a very wide berth. Finally I penetrated his RT and knocked out that AC. I knew I had them then. More jumping around, more dancing, and then I put a gyro hit on him as well. He fell and couldn't get up. Next round I got him with 4 mediums and got his ammo.
Then it was just me and the Archer. By that point, he had one LRM with 6 rounds, and his medium lasers, but he was stripped of armor almost everywhere. I just bounced around and let him shoot at me, usually needing 11s and 12s, and I shot back needing 6s and 7s. Eventually I took off a side torso, and at that point it was safer to be in front of him than behind him. Last round of the game I took off a leg and hit his gyro. He fell and then ejected.
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TL;DR, I have to say it's got a great combination of speed, firepower, and armor for a mech from that time. I ran it against 3025 tech because I figured that's mostly what the Star League was fighting. I didn't take any opponents that were thin on armor or were known for torso bombs. Every mech was a good solid badass.
The Executioner ripped them apart. I definitely have a newfound respect for this mech. If I'd had the Fist Fire ability, and didn't lose initiative two-thirds of the time, this would have been a lot shorter. As it was, it plays kind of like a less ridiculous Black Hawk.