The main idea is to replicate a rogue strengths without beeing a rogue (and also some of an assassin too), like Sneak Attack, Hide in Plain Sight, Poison creation/use, some sort of death attack, and if possible,
sneaking (I mean max "move silently"/Zone of silence/similiar and Hide) , evasion, uncanny dodge and trapfinding (in that order). Like the incantatrix... I have a few options:
>Bard 10/Assassin 10:
the goods: the most basic. BAB +15. Hide in plain sight . Access to Zone of silence (also really helpful), Improvisation (up to 20 "luck points") and Glibness. Bardic Knowledge (10+int). Bardic music (not much useful except for suggestion).
Poison use. Death attack (DC 10+Int base).
Sneak attack +5d6. Improved uncanny dodge. Assassin spells up to level 4.
the odds: Doesn't have access to Polymorph and other useful wizard spells. Can't take 10 when under stress or distracted. No evasion.
>Bard 5/Assassin 9/Teflamman shadowlord 6
the goods: BAB +15. Hide in plain sight . Access to Improvisation (up to 10 "luck points"). Bardic music. Poison use. Death attack (DC 15+Int base).
Sneak attack +5d6. Improved uncanny dodge. Assassin spells up to level 4. Shadow pounce. Shadow walk. Avoid death when in the shadows (with a check)
the odds: Doesn't have access to Zone of Silence, Polymorph, or other wizard or bard spells over 2nd. Can't take 10 when under stress or distracted. No evasion.
>Bard 5/Shadowdancer 2/Assassin 7/Teflamman shadowlord 6
the goods: BAB +15. Hide in plain sight . Access to Improvisation (up to 10 "luck points"). Bardic music. Poison use. Death attack (DC 23+Int base).
Sneak attack +4d6. Improved uncanny dodge. Assassin spells up to level 4. Shadow pounce. Shadow walk. Avoid death when in the shadows (with a check). Evasion.
The odds: Doesn't have access to Zone of Silence, Glibness, Polymorph, or other wizard or bard spells over 2nd. Can't take 10 when under stress or distracted. One less SA dice than the previous one.
>Bard 7/Assassin 9/Exemplar 1/Incantatrix 3
the goods: BAB +14. Hide in plain sight . Access to Improvisation (up to 20 "luck points") and Glibness. Bardic music 8/day. Poison use. Death attack (DC 19+Int base).
Sneak attack +5d6. Improved uncanny dodge. Assassin spells up to level 4. Can take 10 in 1+INT skills (probably Hide and move silently) and +4 bonus to one. Cooperative metamagic, metamagic effect.
The odds: Doesn't have access to Zone of Silence, neither Polymorph, or other wizard spells. No evasion, shadow pounce, shadow walk or avoid death.
>Bard 7/Shadowdancer 2/Sublime Chord 7/Exemplar 1/Incantatrix 3
the goods: BAB +14. Hide in plain Sight. Access to Improvisation (up to 34 "luck points"), Glibness, Polymorph, Shapechange, and other wizard or bard spells up to 9 (CL 17-21 not that bad). Bardic music 8/day. Uncanny dodge.
Song of arcane power. Can take 10 in 1+INT skills (probably Hide and move silently) and +4 bonus to one. Cooperative metamagic, metamagic effect. Bardic knowledge (9+int to the check).
the odds: Doesn't have poison use, IMPROVED uncanny dodge, death attack or SA.
>Artificer 20 (roguish mode)
the goods: BAB +15. Access to almost any spell via scrolls, wands and staffs. Quick access to level 4 or lower spells by paying a low XP cost. LOTS of item creation feats, which gives me easy access to almost any magic item.
Access to SA, Hide in Plain Sight, Evasion, some kind of Death Attack, Greater invisibility and some others via shapechange. Homunuculus for a permanent flanking-buddy. +5 free feats to select among metamagic feats and some creation/item-using feats.
Trapfinding. Easy poison Creation via Shapechange, polymorph, minor/mayor creation, summon monster/natural ally/undead, crafting, planar binding, etc.
the odds: Doesn't have SA, Hide in Plain Sight, Evasion, Poison use, Death attack by it's own. Hide and MS are cross-class skills. Gold dependant. Can't take 10 when under stress or distracted (for skills other than UMD).
>Artificer 17/Shadowdancer 2/Exemplar 1
the goods:BAB +15. Access to almost any spell via scrolls, wands and staffs. Quick access to level 4 or lower spells by paying a low XP cost. LOTS of item creation feats, which gives me easy access to almost any magic item.
Access to SA, some kind of Death Attack, Greater invisibility and some others via shapechange. Homunuculus for a permanent flanking-buddy. +4 free feats to select among metamagic feats and some creation/item-using feats.
Trapfinding. Can take 10 when under stress or distracted on UMD and 1+INT skills. Evasion and Hide in Plain Sight. Can get Hide and MS as class skills at level 10 (need Able learner to not pay 2 points per rank after that)
Easy poison Creation via Shapechange, polymorph, minor/mayor creation, summon monster/natural ally/undead, crafting, planar binding, etc.
the odds: Doesn't have SA, Poison use, Death attack by it's own. Hide and MS are cross-class skills. Gold dependant. 12000 less XP creation reserve, 3 less CL and one less feat than the other option.
>Cleric 15/Darkstalker of Bhaal 5 (this is allowed, even if it's from a DrM):
the goods: BAB +15. Access to Cleric spells up to 9th. Death domain and another domain (Evil, Destruction, Hate, Law). Turn Undead. DMM access. SA +2d6.
Death attack (DC 20+Cha). Bloodthirst (DC 16+Wis). Last breath of Bhaal. It's a nice flavor to worship the God of Assassination
the odds: Not full domain power for death (15d6), Hide and MS are cross-class till getting into DoB. No HiPS, SA, posion use, or other aptitudes. And this time I don't have Shapechange on the list unless I get Planar touchstones (don't know if allowed) or Domain Draught.
Ways to get:
-SA: Assassination aptitude (probably not allowed), Deadly Precision aptitude, Polymorph into Babau or Rakshasa Naztharune, Assassin's stance.
-Poison use: Shapechange into Poison dusk lizardfolk. Beeign a warforged or polymorphed into construct is some kind of poison use.
-Death Attack: Finger of death.
-HiPS: Rakshasa Naztharune (I love this guy)
-Evasion: Ring of Evasion
-Posion Creation: Shapechange, polymorph, minor/mayor creation, summon monster/natural ally/undead, crafting, planar binding, etc.