I'd maintain it's either a CC attack or an unspecified "special" attack, but certainly not a ranged attack as the Callidus' ranged attack is a Template ST8* AP1 attack. (* Resolved against target's Leadership.)
|Warhammer 40,000 Callidus Assassin|
Nice inconspicuous long white topknot thing, etc.
2. Callidus can hit vehicles with the opening "Polymorphine" special rule attack. The Callidus' ranged weapon, the Neural Shredder, can not harm vehicles.
3. Callidus is placed within 3" of the unit, or where the unit was if destroyed. Nothing says a Callidus can't attack a unit locked in CC. No shooting can generally be done against a unit in CC.
4. Let's assume that the Callidus destroys the unit that was locked in CC. Does the friendly unit get a consolidation move? I'm inclined to say no.
5. Rule as written has the Callidus placed within 3" using Deep Strike rules - therefore can shoot but not assault that turn. This is somewhat ridiculous, but I suppose it could conceivably be overpowered if not. Weird. OP-ness must of course be measured against unit cost and synergy with the rest of the codex and weapons and likelihood of swaying a battle and fluff and lore and all that.
EDIT: Rumoured changes coming in 6th edition is Deep Striking units being allowed to shoot immediately upon entry into play. Maybe I'm grasping at straws here, but there's a few possibilities:
A. The rumour is full of crap.
B. Rumour true, but Polymorphine rule changes to make the Callidus essentially stay the same.
C. Rumour true, Polymorphine changes differently or is clarified or Callidus is otherwisely changed (my guess).
D. Rumour true, Polymorphine wording is unchanged, all of a sudden Callidus is looking a tiny bit better. Not good, but better.