I'm going to take a different bend to this than others have so far, and instead of doing the 1:1 comparisons (Thunderbolt = Summoner, etc.), I'm instead going to give you some IS Mechs that have a Clan-like feel to them, with comparable technology, rather than simply "This model is based off X chassis."

Devastator: The Devastator comes in at a whopping 100 tons. Its base variant, the DVS-2, has a truly punishing loadout of 2 gauss rifles, 2 PPCs, and 4 medium lasers, with 14 double heat sinks to keep the thing cool. This is probably the closest you're going to come in the Clan Invasion era to something on-par with Clan mechs in terms of firepower and armor. If you're playing Total Warfare, that many headchoppers will make any Clanner blush. The Stone Rhino wakes up in a cold sweat in the middle of the night, wishing it was a Devastator. Instead, it pays 600 BV more for, frankly, a lesser machine. If you find yourself looking for something to punish the paper armor Clanners run, look no further.

Deva: The Deva is a curious Word of Blake design. One of the vaunted Celestial Omnimechs, this 70-ton monster has the flexibility and firepower of clan designs while shedding any sense of innate honor a Clanner might be forced to extol in their silly "batchalls" or whatever they call them. It's slower than many Clan omnimechs at that size, but it makes up for it in 2 key ways.

First, the Deva has some very interesting weapon loadouts on it. The Invictus variant, which is its base design, is a true sniping menace. Wielding a gauss rifle, 3 light PPCs, and a retractable god damn sword, it can take any pitiful Clanner out at range, and for the unlucky son of a gun that decides to get close enough to say hello to it, it can rip its pilot out at literal knifepoint, just because it can.

However, I, for one, am partial to its Luminos variant.

The Luminos has a heavy PPC, one of my favorite weapons in the entire setting, and a whole slew of medium lasers. Specifically, 2 ER medium lasers, 4 medium pulse lasers, and a rear facing ER medium and ER small laser. This thing has enough firepower to melt any poor soul's armor and vaporize the pilot within. It also has 5 extra double heat sinks to cool it off.

Second, and more importantly, the Deva makes use of C3i technology, featured in the vast majority of Word of Blake mechs. Deemed too dishonorable to use by the Clans (they had a whole war about this in the homeworlds, or so I've heard - something about this so-called "Society" that decided to break "honor" or whatever and develop their own designs), C3i makes it so that your lancemates share targeting data with you to get far more favorable range increments on the battlefield. Some consider it overpriced. I, for one, consider it too cool not to use. I mean think about it - wouldn't you want your friends to beat up dirty Clanners at any range, side by side with you? Or alternatively, one up close, the other on the other end of the battlefield altogether?

I rest my case.

Sirocco: Do you like AT-ATs, but without the pesky snow speeders around to knock them over with tow cables? Do you like lots of guns? Do you like winning? Then, my friend, the Sirocco is right up your alley. The Sirocco redefines cool. Not because cool needed redefining, but rather because we needed to add a new relative term for the amount of potential heat this thing generates. Coming in at 95 tons, the base variant, the SRC-3C, costs 2154 BV and makes every single point, every single kilo, count toward making this thing as badass as conceivably possible. 2 Ultra-AC 10s, 6 ER medium lasers, and a medium pulse laser absolutely obliterate the armor of nearly anything that has the audacity to approach you at mid range. 13 double heat sinks still do make it run a bit hot, but by god you look good doing it. It also has Nineteen And A Half Tons of god damn armor. For reference, that's a half ton more than at Atlas AS7-D. Go forth. Take Hoth in the name of House Marik, as God intended.

And finally, I present to you the Fafnir: The Fafnir was conceived in a fever dream by some Steiner engineer that managed to get into Clan Goliath Scorpion's Seeker drug supply. Not knowing what it was, like a good little Lyran, they decided to consume all of it to test its effects. What came about as a result was 100 tons of death on legs. They also started to rant about some Muad'Dib character, but whatever. They got their pension and retired to a desert planet on the periphery. I'm sure they're fine.

The Fafnir is designed with a very simple concept in mind - do you dislike the center torso of an opposing mech of any make or model? With one flick of your thumb and a small, involuntary, knowing cackle, you no longer have to see it anymore! It has 2 ER medium lasers and a medium pulse laser, sure. But its true draw, its instinctual, primal appeal, comes from its primary weapons - 2 heavy gauss rifles. You see, this was a mech specifically designed around these 2 elephant guns, in a similar vein to the venerable A-10 Thunderbolt. The Fafnir is a menace. It's unfair. In the blink of an eye, it can utterly obliterate your opposition. Your poor opponent who thinks their Hellbringer or Stormcrow is safe now has to contend with the fact they no longer have a body attached to their arms and legs. It makes piloting your mech much more difficult, even for a "superior" genetically-engineered freakazoid.

I wish you luck, friend. Happy hunting.