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I saw this in the FAQ but it wasn't really addressed fully. The basic idea about what I'm thinking is that you take a tomb spyder and make a scarab swarm. This gives you a unit with 5 wounds @ T6. Since this is a mixed unit with more than one model, you are able to add an independant character to this unit (i.e. Necron Lord). Since you now have 3 models in the unit, you are able to add an additional swarm scarab to this unit giving you 11 wounds @ T6 for your Necron Lord + Tomb Spyder. You would probably want a warscythe on your Lord as this unit will be pretty strong in CC, but a staff of light wont be bad either assuming you have your TS leading your phalanx accross the board (plus you could have your RO for the immortals/warriors behind this unit).
I'm just wondering if this tactic would have any practicality/usefulness, or would you be better off with your Lord somewhere else doing something else (also possible out of LoS).
It is still debated wiether you can join a Lord to the Tomb Spyder w/ 1 Swarm since MC normally can't be joined by ICs and the Spyder doesn't actually say a IC can join them now
Also adding a Lord doesn't let you get away with another Swarm since the Majority would then be T3 (there are 2 T3 models is a mojority over 1 T5 model and 1 T6 model)
Your lord would require a destroyer body to be T6 himself, then majority toughness could kick in again. The question is whether this is useful by any means. Now you have a very slow unit that has T6 against shooting attacks (while wounds allocated to the scarab bases still impose instant death with S6 or higher). In close combat your lord fights on his own, leaving the rest of your unit at majority T3. I don't see the great gain in this.
As far as the IC joining the group, the ruling for IC says:
"They cannot...join...units that always consist of a single model (like most vehicles and monstrous creatures)." (4
Since the tomb spyder unit is not a unit that ALWAYS consists of a single model, I would think that it is appropriate for a lord to join this unit.
As far as majority rule:
"To keep things simple, roll to wound using the Toughness value of the majority of the engaged foe. If no majority exists, use the highest value in the unit." (3, (similar for shooting on page 19).
This to me means that a majority of the unit has to be a certain toughness, and in this case 2/4 is not a majority even though the other two differ in toughness.
I did overlook the part about ICs being singled out during assaults, which would make your tomb spyder + 2 scarabs have T3, which would be pretty bad. So you would really only have a Necron Lord + Tomb Spyder + 1 scarab swarm, which I'm not sure helps that much. As far as Instant Death goes, you would have to wound on the unit's T6, but you would take the scarab's unmodified T3 to determine if it was instant death?
Yes, you definitely use the scarab toughness for instant death purposes. Your opponent rolling to wound on majority toughness has nothing to do with actually changing the toughness value of the scarab model, which is used to determine instant death [page 26, big rulebook].
[And as for the term "majority": where are you from? UK or not UK? In American English the term majority is used to describe a subset that is more than half the entire population. In British English, though, (which is the dialect the rulebook authors use) majority is used as a synonym to what in American English you would call a plurality, a word describing simply the largest subset in a group. Thus, being no native speaker, I will not make a call in this case.]
Yeah I am not from UK (live in USA), so majority to me means strict majority. I can see how this can be applied to a plurality sense, so I guess the rule would just be applied locally in different ways. Either way, the point seems to be moot as even if you do have two scarabs in the unit, once you engage in CC, your lord is considered a separate unit, and your TS would be brought down to T3, which is pretty bad. So, in you're unit you would have one lord, one TS, and one scarab swarm. The benefits to this would be giving your Lord T6 without having to upgrade to a destroyer body (only in shooting as in CC he is treated as a separate unit), and giving your lord and TS 3 extra wounds total. There really doesn't seem to be an advantage to this except for possibly giving your lord T6 (and some extra wounds) from shooting while moving up the field. It seems that he could be better suited out of LoS behind your TS or doing something else like Flying Circus or just as support.
Forget the tomb spyder and give him a destroyer body and phase shifter instead. Warscythe is almost a must. Then he is a very formidable unit on his own. If you can afford a wing of scarabs to shield him from shooting attacks or a wing of wraiths to accompany him and help him wreak havoc, you will be more than pleased.
Yeah, I'm not too sure what the appeal would in attaching a lord to a tomb spyder (presuming one can do so). Yes, you'd get MC attacks in a unit, along with the lord's PW or warscythe but its kind of pointless if you're just looking to shield him from shooting by giving more wounds. A wing of scarabs would be easier and more mobile when attached to a D body lord.
Necrons W68-D13-L10 (3rd edition codex)
Necrons W3-D1-L1 (latest codex)
Skaven still being assembled