Generally, when I've found assassins most useful, I've went for quantity, not quality. As Atlantis, 5 Tupilaks a turn can mess with an opponent's plan. As a nation who can recruit assassins, I think the key is not to use them to soon. Once you start using them, your enemy gets cautious and careful with bodyguards. Instead, try to gather five or ten to a key province, depending on your economy and number of target provinces.
Key provinces... research centers, if you can take em all out. Armies sieging one of your castles (any units dedicated to patrols are NOT tearing down your walls. Best yet, assassinate as many leaders of an invading army as you can while your army is nearby. If they're light on spares, then you'll split their forces in two. And if you're attacking that province (with a scout, even, and the rest of their forces moved out) the unled troopers left behind will rout and scatter further.
After you do this, the bodyguards will be on hand, so it better be a critical moment, unless you have super powered assassins. You sometimes can still assassinate after this, but your loss rate will be higher. With capital only assassins...
One of the more overkill, but effective asssassins I've seen. Only once, for some reason. I don't think you need to go this far.
Now, as you're playing Ctis, you'll probably be facing some priests, since skellyspam is expected. I don't suggest the following tactic once your up against player nations. A Skull Talisman can give that indy mounted commander a couple other things to charge. It gives you one skeletal bodyguard and lets you summon additional ones for 5 fatigue. Script a couple casts, then attack as normal. (You don't want to cast only, or else you'll be out of luck when facing a priest)
A few Empoisoner ideas
D2 Spells castable with gems (pref), or boosters.
Disintegrate (alt 8) (prec 100) + penetration items like Eye of the Void
Raise Skeletons/Dead (ench 3)
N2 spells as above
Storm of Thorns (evo 7) - enough projectiles you might actually hit something, especially if you have the time to cast Eagle Eye (Agartha, Abysia, slow races w/o cavalry)
Sleep Cloud Evo3, Sleep Thau2. (cloud
Forty-six fatigue approximates -4 def, -2 attack for them, whereas you get a -2, -1 penalty. If you can hit them several times, sleep. Perhaps summoned skeletons to tie them up? (regular
110 fatigue equals sleeping target. First problem is its single target, second problem is that both sleep spells can be resisted by MR- not a good thing at all, though with astral randoms comes penetration items.
Untouchable Miasma of Death (construction four)
Snake Bladder Stick
Raw Hide Shield
Cat Charm
Scripts - Attack
Defense - 20
Total Nature Gems - 20
EDIT:
This build is uncomplicated and pretty effective. The high defense means most crappy bodyguards can't touch you while the area-affect poison works.
Ironically, wild carnivorous lizardmen can take you down. They tend to bodyguard their shaman, and have two attacks per warrior, meaning -4 def per attacker. Be careful around them, and avoid them if you skipped the Cat Charm.
[/EDIT]
If you're on a budget, you can just equip the Raw Hide Shield (con 0, 5 gems). It'll let you keep and use both your weapons. Equip two shields and you get a Useless Kick, though you can still spellcast and sling. A Thorny Staff will get you slightly better defense as well as some extra attack, but has its own downsides.
On the other hand, if you want to scale up, there's the Vine Shield, Totem Shield, and Eye Shield, all of which also have zero defense and encumbrance penalties.
There are other things to consider, such as Skullface, and Wraith Crown, if you've got to many gems for your own good, and theres' a lot out there depending on what independents you find.
The most absurd, but mildly plausible combination I can imagine involves (The Ankh - automatic life after death), Carcator the Pocket Lich, Sandals of the Crane (blink), Wraith Crown, Robe of Missile Protection, Treelord's Staff.
Script? Creeping Doom for 70+ ants.
I'm tempted to actually put this together just to see what kind of zombie, if any, 70 ants make.