Sister Stern wrote: 1. If a Eldar wave serpent moved less than 12 inches and gets immobilized thru opponent shooting, is the Wave serpent destroyed or does it just "land" on the ground and you remove the flying bases? Does going "flat out" speed make you crash/destroyed if immobilized?
Moving Flat Out (more than 12") in the previous turn causes the skimmer to crash on an immobilised damage result. Covered in the 'Shooting at Skimmers' section on page 71 of the rulebook.
Moving less than 12" would just cause a normal immobilised result.
2. The Wave serpent has skimmer and fast for vehicle type, I think it has different inches for going "flat out" speed (24 inches for skimmer and 18-24 for fast.), which one should you go by?
It's a Fast Skimmer, so you use the Skimmer movement rules, which list the specific speed for Fast Skimmers.
The Fast vehicle rules apply to all Fast vehicles. The Skimmer movement rules for fast skimmers apply specifically to Fast vehicles that are also Skimmers.
3. The twin-linked shuriken catapults underneath the Wave Serpent is hull mounted so does it have a 90 degree shooting zone facing forward or 360?
Hull mounted weapons have a 45 degree fire arc.
However the Serpent's catapults are not actually defined as hull-mounted, and can pivot if they're not glued in place, in which case they get whatever arc they can physically move through.
Additionally, the Rulebook
FAQ says:
Rulebook FAQ wrote:...In the same way, the
shuriken catapult mounted under the hull of a
Wave Serpent, Falcon, etc. looks like it can rotate
360º, but it does not look like it can be fired
through the main hull right behind it, so we
normally play that it can be fired roughly in the
180º to the vehicle’s front, which seems like an
acceptable compromise.