Originally it did have Nemesis attracting Homing A4, but that changed between versions IIRC but I looked at that a couple of weeks ago for the EWar mech discussion. Nemesis gets more useful if you expect to run into someone spamming Semi-G . . . It does not specifically address some of the TacOps ammos or gear- Artemis V, Apollo FCS, ARAD missiles though ARAD's behavior with NARC pods implies it works with Nemesis.
It never attracted friendly Arrow IV. I understand why they did it. They probably felt like being able to TAG someone, permanently, at least until they knock the beacon off, was a bit OP.
TM w/ the Battlemaster cover, 3rd Printing
Originally for hostile NARC munitions, upgraded to include attracting Artemis IV, Semi-G and A4 homing from friend or foe- it does not say anything about LOS
TM w/ retro cover, 3rd printing?
Same, nothing about LOS.
Thing is, nothing in the TM entries tell me how that works- does it roll up like Swarm?- and I cannot find descriptions in other places or how to determine the hit. A4 & LOS from the Sarna (citing FM ComStar) requirement made no sense to me, most homing is fired IDF which means technically no LOS so the wording in TM is better. The way TM reads to me is it attracts any missiles in range on the whole map.
Tech Manual is just build rules with a few usage rules that snuck in when no one was looking. Battlemech Manual 108, or TW 142 have Nemesis rules.
The first two conditions for Nemesis are that the Nemesis tagged unit is along LOS between the shooter and the target, and that a valid LOS exits between the shooter and Nemesis tagged unit, (BMM 108). But after posting a rules question, it only applies to units EXACTLY on the LOS. Say A & B are friendles and C a hostile, 20 hexes away on a dropship tarmac. Assume A and C are facing each other's front and the LOS is dead vertical. B move to C's #2 hexside, at 1 hex range, where C hits it with a Nemesis. In this case, B has nothing to fear, because it's not directly in line from A to C.
So even if the other side is spamming Semi-guided, Artemis, or Narc, I still question the effectiveness of Nemesis because one hex left or right will take the Nemesis unit out of the LOS from shooter to target.
Swarms are covered in TO, pg 371, but the short version is that any LRMs that don't hit the primary target, try to attack anything else in the target's hex or any adjacent hex, with the remainder of the flight. Secondary targets are attacked using a To Hit penalty. So as long as the enemy maintains 1 hex separation, Swarms are no better than regular LRMs. Also, Swarms don't much care who they attack, friend or foe. So could very easily earn the emnity of a Berserker pilot by using Swarms on a mech that she's trying smash. Swarm-I mitigates that some with an IFF modifier.