Posted 20 December 2015 - 02:44 PM
^^^ Rogue Jedi pretty much said it all.
Sorry, I might get a little long-winded here.
See, when we first got this game in beta, well over three years ago, there were ONLY IS battlemechs. There were no Clan mechs, and we really didn't know when we would see them. So, we all got into the best practices of laying out IS battlemech builds.
Along comes the Clan invasion. Waves I, II, and III were all Clan OMNImechs. Those are the ones with hardpoints and some locked equipment fixed in the omnipods. They are front-line, first-to-fight kind of equipment for the Clans.
The IS fought back, with the Resistance I and II battlemechs (as the kinda-sorta-divergent MWO timeline goes). Ignore Urbanmech, as that was PGI giving in with a very heavy sigh to our demands that the infamous little trashcan be added. And it is loved by many.
And now, especially given some IS counterattacks against Clan-held territory, we have the II-C variants showing up. As you've no doubt read above, those are Clan-reimagined IS battlemechs.
The physical differences in-game for us?
IS battlemechs use only IS equipment and do not use omnipods.
Clan omnimechs use Clan equipment and DO use omnipods.
Clan battlemechs (II-C) use Clan equipment and do not use omnipods.
Clan tech is generally lighter and smaller than IS tech. Engines are the exception to the weight, where a Clan and IS XL engine of the same rating also weigh the same (but the Clan XL is two critical slots smaller). Clan lasers have longer durations and produce more heat, but also generally do more damage and have a longer maximum range, than IS lasers of the same class. Clan energy weapons do not have 'regular' versions; there are only ER and pulse lasers, and only ER PPCs. Clan NARC has a longer range, too, IIRC. Clan armor, at least the FerroFibrous stuff, is a little bit lighter, too. And IS mechs have QUIRKS, making some of them heavily specialized for certain situations or weapon systems.
That's about it.
I want my Locust II-C now.