So I'm trying to figure a couple of things out as some may have begun to notice. Specifically concerning technomancers. I'm running into a few small problems as I hash out ideas and scenarios for my and other players' use of their sprites abilities:

1. Diagnostics from the Machine Sprite: Is that considered a sustained ability? Does it continually modify the dice pool modifier if I were to, say, have it run diagnostics on my friendly street sam's assault rifle?

2a. Really, I'm thinking about multi-ing up as a street doc or even a surgeon (no, really) in a quick fix (someone not too long ago mentioned doing surgery stuff for other runners with the right drone equipment, kinda perked my interest) and using a Machine Sprite to sustain the diagnostics on the medical kit or drone or what have you.

2. Castling. Okay, I get that you have to first use a simple action to call up the Paladin Sprite or use up a Complex action to create one. Then, on the Paladin Sprites first initiative pass (the next one, presumably), your Sprite can Castle your ID. Can it then sustain that and then use Harden (or, for that matter, vice versa?) of which it is then sustaining both of its powers?

2a. For the Paladins, I'm trying to figure out the awesomeness they bring to the table, especially if the cybercombat situation is a prolonged fight. Like say you're going up against a hacker/TM with 4 or more IPs. The Paladin sprite would eventually run out of IPs to go: Okay, I'll Castle/Harden up again. I mean, during the time that they're able to actually Castle up, they're insane. I mean, even with a rank 5 Paladin Sprite (I know, who in their right mind has a rating 5 sprite!) you're rolling something like 19+ or so dice for defense (off the top of my head: 14 for Response + Firewall and 5 more from Shield I guess you could use Expert Defense for more dice ).

3. The one ability I think I'm clear on that is sustained is the Electron Storm from the fault sprite that specifically states the sustained action.

Finally, thanks in advance and if possible, any help with explaining the answers in a way so I can then explain the answers to other people without sounding like a jerk would be helpful. <-- I'm usually pretty good at not sounding like a jerk, but still.

Read up on Sprite Tasks. p. 240 - 241 SR4A

"Continuous use of a specific power, whether on a single target
or a group, counts as only one task. If the parameters of a task are
changed, another task is used. Engaging opponents in a single node
in cybercombat only counts as one task, regardless of the number of
foes involved."

Also read Registering Sprites.

1. Sustaining a power is one task. Yes it would continually modify the dice pool.

2a. Yes.

2. Castling requires a complex action, Hardening requires a complex action. Each is a complex action. It's not a complex action to turn on and then it keeps going for free. So in one complex action you can get one or the other, but not both.

2a Take a look at the Transfer Power.

Ah, thanks for the continuous use thing. I knew I had read it at some point. I must've been reading past it over and over again since then. So that would make another interesting situation, since:

On 2. Both Castling and Hardening happen to be powers which means both can be sustained. First initiative pass that the Paladin is Available: Castle up. Second initiative pass: Hardening. Both powers would then be sustained as it is a continuous use of of the Paladin's power in order to: "Defend me to the best of your abilities. Right? Am I finally wrapping that around my head?

Sidenote: I know that both are complex actions, but they are also sustained actions (as noted in the excerpt you gave me). I was mentioning that it took a simple action to call them into the node.

Thanks for the help and pointing out the rule I had lost over the past week DireRadiant.

Castling
"Named after the chess move, a sprite using this power with a
Complex Action can redirect damage targeted at the technomancer
to itself by temporarily mimicking the technomancer’s access ID."

Hardening
"A sprite with this power can temporarily empower its Armor
complex form to become like Hardened Armor (p. 288, SR4), allowing
the sprite to soak damage from most sources as long as it
continues to use the power. Using Hardening counts as a Complex
Action, similar to going on Full Defense."

It's all subject to interpretation of course, but it's hard to see any actual use of either power not taking both sustaining, and an actual Complex Action. That is I think they consume a Complex Action each and every time the power is mechanically involved.

Then this would also carry over to Diagnostics as it is a single teamwork roll instead of a sustained task. The only power that I see that has the word sustained in it is the Fault Sprite's power. From the way Tiger Eyes described it and others clarified it a while back was that usually one ability would be activated, then the other. The word Sustained was around and I couldn't find out how sustained came into the picture until you pointed it out to me. It was also noted that the designer of the Sprite section of Unwired intended for Hardening and Castling to work together.

And they couldn't take up both a sustained and complex action. If it is a sustained action, then they sustain it just like a mage sustaining their magical power who then casts a second magical power while sustaining the first. He can then sustain both powers (Invisibility and Magical Armor or something). I don't see how it would be different for a sprite.

There are no "Sustained" actions.

"The Diagnostics power allows the sprite to evaluate the inner workings
of an electronic device. The sprite must be present in the node of the
device in question. The sprite can then assist someone using or repairing
the device with a Teamwork Test. Make a sprite rating x 2 test;
each hit adds 1 die to the character’s test to use or repair the item. The
maximum dice bonus the character can recieve from the teamwork test
is equal to that character’s skill."

Note that Diagnostics does not anywhere refer to including a Complex Action as part of the power functioning, while both Castling and Hardening explicitly include a Complex Action in the description of how the power works mechanically.

In any case, it's up to you, unfortunately SR4 doesn't have the mechanical framework and definitions modeled to the level to get a definitive feel for how all the individual powers work regarding the actions so just do what you think is best for your game.

edit: Unlike Spirit Powers, there's no generic Using a Power takes a Complex/Simple/Auto Action statement, so we are left with the individual descriptions.

So, neither hardening and castling can be sustained (all of the protective abilities in the spirit section are sustained or permenant to include Hardened Armor which is listed as 'always' and Guard (the closest thing I could find for Castling) which is sustained). So the ways that have been explained in the past are all incorrect. Yes, the powers specifically state that they require a complex action to activate. He power would then be active until it is then inactive.

You are right, Diagnostics doesn't state that it requires a complex action to use, but it is still not a sustained power if we were to base the situation with Castling with the situation with Diagnostics. It does however state that Diagnostics works like a Teamwork Roll, which is a single test Unless it is noted that the action is an extended test. Shooting someone is not an extended test, so therefore it would still need to be reactivated each time in order for it to be used.

Either they all operate the same way, or they all operate as a single action that must be activated each time.

And you're right there is no 'sustained actions'. There are powers that are sustained.