The more detail you provide, the better we can help.
Sadly, the tome of magic version of the dark template has a significantly worse version of hide in plain sight then shadowdancer's. If you can convince your DM to use the Cormyr version instead (I can't recall which was published later, ToM or Tearing of the Weave), you're golden.
ToM: March 2006.
Cormyr: March 2007.
Also, I couldn't link this earlier, but Surreal's Lists of Stuff deserves a mention:
Hide in Plain Sight (or similar) (also see the "camouflage" section)
Ranger 17 - natural terrain
Scout 14 - natural terrain
Illusionist 15 (class variant), Unearthed Arcana - unconditional
Assassin 8, ecl 13 - within 10 feet of a shadow
Shadowdancer 1, ecl 8 - within 10 feet of a shadow
Nightsong Infiltrator 10, ecl 17 - natural terrain
Dark Lantern 9, ecl 14, Eberron: Five Nations - does not require natural terrain or concealment, in fact seems totally unconditional
Scar Enforcer 7, ecl 12, Races of Destiny - natural terrain
Wildrunner 5, ecl 10, Races of the Wild - natural terrain
Stalker of Kharesh 4, ecl 9, Book of Exalted Deeds, w/quarter cover or quarter concealment
Wilderness Rogue (UA)
Umbral Disciple 3, ecl 8, Magic of Incarnum, see text
Luiren Marchwarden 5, ECL 10, FR: Shining South - doesn't require cover or concealment, but only works in specific region
Shadar-Kai, race, Fiend Folio, ecl 4
Dark creature, template, Tome of Magic - doesn't require cover or concealment or terrain, but doesn't work in bright light
Shadow Creature, template, Lords of Madness - in shadowy regions only
Lurking Terror 3, ecl 8, Libris Mortis - requires cover or concealment
Paladin 6 (Shadow Cloak Knight substitution level), Champions of Valor web enhancement - near shadows
Justice of Weald and Woe 9, ecl 15, FR: Champions of Ruin - natural terrain
Planar Touchstone (The Veil), feat, Planar Handbook - near shadow
Hellbreaker 1, ecl 6, Fiendish Codex II, in any kind of darkness, not called "hide in plain sight"
Shadowspy 9, ecl 13, Complete Champion, in area of sunlight
Sentinel of Bharrai 5, ecl 10, Book of Exalted Deeds, within 10' of natural terrain
Eye of Lloth 6, ecl ?, Drow of the Underdark, within 10' of shadow
Ebonmar Infiltrator 8, ecl 13, Cityscape
I guess I will inform my friend that he should just stay in assassin. He wants to reliably deliver sneak attacks.
This is why it's always best to tell us the whole story from the start. The most reliable way of doing this isn't stealth (action-intensive in the middle of combat and easily foiled by a large number of abilities), it's flanking (easy to set up, action-independent, and only really foiled by a very small number of abilities, of which only improved uncanny dodge is common). He can even flank by himself by grabbing Distracting Ember from the Tome of Battle - you say he's already a swordsage.
Speaking of:
He has assassin stance from 1 level in Swordsage.
This is impossible. The first level of any martial adept only grants 1st level stances, regardless of your initiator level. (Carefully read the stance text again - it's different from the maneuver text!).
This isn't usually a big problem for swordsages, though, since they get their second stance at level 2 and their first-level stances include some very good options. For sneak attackers, the best first-level stance is probably Island of Blades - not only will it work with the Shadow Blade feat you mention, it sets up more frequent sneak attacks simply by letting you flank targets from more positions.
By the way, what I mentioned above about stealth being less useful in combat? Swordsages can learn Cloak of Deception, which gives you one round of improved invisibility as a swift action. That gives you all of the benefits of stealth (with slightly better anti-detection measures), but at a dramatically improved action economy (the cost is lower and the stealth effect lasts throughout your attacks). If your IL is high enough to consider Assassin's Stance, then you're high enough to have learned Cloak of Deception.
He has Craven and Shadow Blade. I'm attempting to advise him of TWF but idk if he'll go for it.
Purchase Gloves of the Balanced Hands. This can let you get the benefits of Improved TWF without actually going through that expensive feat chain. If you want TWF to work in battle, you'd be better off focusing on mobility options (Sudden Leap is a cheap example, also available to swordsages; there's a lot of inexpensive items (i.e. Acrobat Boots, MIC) which also allow swift-action movement), as these effects will allow you to be in melee range with an available full-round action (the basic way to get multiple attacks, and thus multiple sneak attacks).
Finally, you'd be better off here looking for accuracy than raw damage. Assassin attack bonuses aren't terribly high, and a sneak attack that doesn't hit doesn't do any damage. A typical core/ToB way of boosting this up is to use Swords of Subtlety enhanced with the Martial Discipline (Shadow Hand) ability - that's +7 attack, +4 damage on each attack you make while making sneak attacks in a Shadow Hand stance, on top of whatever else the weapon provides (including its enhancement bonus and the Shadow Blade feat). If you can get them built using the Feycraft template (DMG2) you also get the benefits of Weapon Finesse without actually spending the feat on Weapon Finesse; since you're already getting Shadow Blade (which counts as weapon finesse for prerequisites), this is unlikely to screw up your feat timing at all (unless you used Weapon Finesse as a prerequisite for something before grabbing Shadow Blade, but this is unlikely). If you want to really cheese off your DM, fit one of the swords with a wand chamber and a wand of Wraithstrike (SpC), turning those attacks into touch attacks.
(The only remaining problem after you consider accuracy and trigger conditions is fortification - and there are cheap ways around some of the more common ones available to you. The MIC has inexpensive augment gems - truedeath, demolition, etc - which allow you to sneak attack commonly immune creature types. (This is more economical, but harder to switch on the fly, than the SpC's vinestrike, gravestrike, and golemstrike spells.) They're not exhaustive, but you shouldn't forget about them.)
I'm less familiar with the Unseen Seer than I'd like, so I can't comment on that except to say it has a good reputation and, as I recall, it deserves it. If you can afford the route, I'd definitely consider it.
Our DM is permitting fractional BAB but not LA buy-off. We're lvl 10 and it's close to time to play so I have to get the character ready in time. Nightsong inforcer is also a strong option.
None of this changes anything said earlier in the thread (and although nightsong enforcer has a strong skeleton - full base attack and almost full sneak attack will do that - its entry requirements make it kind of unappealing).
A basic 10th level sneak attack build that must include Assassin levels might look like this:
Human, 10/15/14/13/10/8, +Int at 4, +Dex at 8
1 Rogue 1 (TWF, Improved Initiative)
2 Swashbuckler 1 [Weapon Finesse]
3 Swashbuckler 2 (Craven)
4 Swashbuckler 3
5 Rogue 2
6 Assassin 1 (Daring Outlaw)
7 Swordsage 1 (Cloak of Deception, Wolf Fang Strike, Sudden Leap, Distracting Ember, Moment of Perfect Mind, Sapphire Nightmare Blade) (Island of Blades) [Discipline Focus: Shadow Hand]
8 Swordsage 2 (Shadow Garotte) (Assassin's Stance)
9 Unseen Seer 1 (Shadow Blade)
10 Unseen Seer 2
Weapons: two +1 Shadow Hand short swords. You can't afford twin swords of subtlety at 10th but keep it in mind. Including Swashbuckler means you don't need Feycraft. (It also helps improve your attack bonus and lets your Int do more than boost spells/death attack; Daring Outlaw can be viewed in this build as a second copy of Assassin's Stance.)
Other gear: +2 gloves of Dexterity, basic defensive kit. Gloves of the Balanced Hands and augment gems if you can swing it.
Finishes with +8 base attack (melee +17 / 1d6+7(+7d6+10 sneak attack) with a single short sword in Assassin's Stance); you can figure out the rest on your own.
Note on maneuvers I didn't mention above: Shadow Garotte lets you deliver sneak attacks at a distance with a touch attack, SNB allows you to catch targets flat-footed with just a skill check and the attack itself, and WFS allows you to move and attack with both weapons.
[You can get into Unseen Seer with Assassin if you've got 12+ Intelligence and learn Detect Poison and True Strike, although there are probably better divination options in the SpC.]
[Likewise, Improved Init is there because I'm being lazy and can't think of a better option off the top of my head. A cheap possibility is to copy the Gnowhere Gnome's trick and grab Evasive Reflexes instead; at 12th you can get Shadow Stalker (PHB2) and slink around while invisible with almost no risk of being spotted if you're clever.]
You can probably do a lot better than this with tweaking, but you shouldn't be doing worse than this.
Improved initiative is a good feat for a rouge character though.
I thought all short swords were shadow hand weapons.
In ToB, there is a new weapon enhancement called Discipline. Get that, and key it to Shadow Hand. That's what TS meant.
Improved initiative is a good feat for a rouge character though.
Why is his character red? I imagine that can't be very stealthy.
Improved initiative is a good feat for a rouge character though.
Why is his character red? I imagine that can't be very stealthy.
Shanking people is a messy business.
im not really familiar with the incantrix, bur wraithstrike and greater invis are target: you, so you cannot cast it on anybody else
Someone here has never seen the Twice-Betrayer, or really any optimized Incantatrix.