Words like "low level" aren't particularly helpful here. Best to give some hard detail. I'll see what I can come up with.
hrmmmm, undead lord gnome? With a Dhampir progeny? interesting....
Alchemist and Arcanist come to mind easily enough, unless maybe a Cleric of the Whispering Way? Throw your party for a loop and make him a multiclass with an Alchemist Dip with a Cognitogen... Boost that spellcasting stat! Maybe make him a Bleachling, so he's seen the "end" and wants to keep his "daughter" from it, and he's getting into Alchemy as another way to the same end?
He'd need a good support team, so maybe:
1) the Chief of a local humanoid clan as local mooks and muscle. Recommend keeping them small to challenge the medium races. Kobold/goblin/grippli?
2) A relative of the gnome (true or adopted) who's into the same thing because he enjoys hurting things in imaginative ways, maybe an Alchemist teacher?
3) "Mr Fixit" - the sniper or assassin to get problems solved. Ranger or Rogue? arcane trickster?
4) the Dhampir. Just because she's a child doesn't mean she's helpless.
5) Familiar. Given enough rank in the scheme of his life, he could be a sergeant for mooks to taunt the players for a few encounters.
6) One random unintelligent big-azz monster at the bottom of the nest to throw things into for entertainment and waste disposal. Ooze, otoyugh, gelatinous cube farm, uncontrolled zombie stock pile, rust monsters, get creative.
Then, if you want to challenge them with "mid level" challenges, give them flying opponents (flying monkeys?), spellcasters with buffs / debuffs, things that can go through walls (incorporeal or small earth elementals), or things that would act like players. How would your players try to take themselves out? Do they have a weakness to exploit? Anything from an earlier adventure that would join with Mr. Evil to kill the good guys for fun and profit?
Just my 2cp.
A stat block for a gnomish undead focused alchemist. The "Reanimator" archetype might be appropriate here, but I forewent it as you can get much the same effect from taking the right infusions.
In addition to making alchemical zombies and using boneshard bomb, the alchemist uses confusion and stink bombs, as well as poison and alchemical items, to sow confusion among its enemies.
Nivgendal
Male Gnome alchemist 9
CE Small humanoid (gnome)
Init +2, Senses low-light vision; Perception +15
=================================================
DEFENSE
=================================================
AC 16, touch 13, flat-footed 14 (+3 armor, +2 Dex, +1 size ); +4 dodge vs. giants
hp 67 (9d8+28)
Fort +11, Ref +10, Will +8, +8 vs. poison
=================================================
OFFENSE
=================================================
Speed 20 ft.
Melee dagger +6/+1 (1d3-1 plus poison/19-20)
Ranged bomb +10/+5 (5d6+3)
Ranged masterwork crossbow +10 (1d6 plus poison/19-20)
Special Attacks +1 on attack rolls against goblinoid and reptilian humanoids, bomb 16/day (4d6+3 fire; DC 17)
Gnome Spell-Like Abilities (CL 9th; concentration +10)
1/day - bleed (DC 11), chill touch (DC 12), detect poison, touch of fatigue (DC 11)
Alchemist Extracts Prepared (CL 9th)
3rd-burrow(2), gaseous form, undead anatomy i
2nd-barkskin, false life, invisibility, resist energy, see invisibility
1st-bomber's eye, cure light wounds(DC 14), detect undead, expeditious retreat, identify, shield
=================================================
STATISTICS
=================================================
Str 8, Dex 14, Con 16, Int 16, Wis 12, Cha 10,
Base Atk +6; CMB +4; CMD 16
Feats Brew Potion, Extra Discovery (2), Iron Will, Point-Blank Shot, Precise Shot, Throw Anything
Skills Craft (alchemy) +17, Heal +13, Knowledge (arcana) +15, Knowledge (religion) +12, Perception +15, Spellcraft +15, Use Magic Device +12
Languages Common, Gnome, Goblin, Kelish, Osiriani, Sylvan
SQ alchemy (alchemy crafting +9, identify potions), bonus bombs (9x), discoveries (alchemical zombie, boneshard bomb, confusion bomb, precise bombs, smoke bomb, stink bomb), fell magic, mutagen (+4/–2, +2 natural, 90 minutes), poison use, poison use, swift alchemy, swift poisoning
Combat Gear wand of inflict light wounds (50 charges), blue whinnis (3), giant wasp poison (3), large scorpion venom (6), purple worm poison (2), potion of barkskin +2 (2), potion of cure light wounds, potion of invisibility, potion of resist energy 10 (electricity), potion of resist energy 10 (fire), tanglefoot bag (3), liquid ice (3), acid (3), alchemist's fire (3), bottled lightning (3); Other Gear masterwork studded leather, dagger, masterwork crossbow with 20 bolts, cloak of resistance +2, handy haversack, hybridization funnel, alchemist's lab, alchemist's kit, formula book, healer's kit (10 charges), 20.0 gp
=================================================
Formula Book
=================================================
Alchemist Spells
3rd -burrow, gaseous form, undead anatomy i
2nd -barkskin, false life, invisibility, resist energy, see invisibility
1st -bomber's eye, cure light wounds, detect undead, expeditious retreat, identify, shield
=================================================
SPECIAL ABILITIES
=================================================
Alchemical Zombie (Su) You gain the ability to animate a relatively complete corpse as an alchemy-powered zombie. This process takes 1 hour and costs 100 gp in alchemical reagents per HD of the corpse being animated; the dead creature gains the zombie template. Zombies that are created in this manner count as undead created by Animate Dead for the purposes of determining how many undead the alchemist can control. The created zombie is a creature, not a supernatural effect.
Alchemy (Su) When using Craft (Alchemy) to create an alchemical item, you gains a +9 competence bonus on the Craft (alchemy) check. In addition, you can use Craft (Alchemy) to identify potions as if using Detect Magic. He must hold the potion for 1 round to make such a check.
Bomb (Su) You can use 16 bombs each day. Bombs are considered weapons and can be selected using feats such as Point-Blank Shot and Weapon Focus. On a direct hit, your bomb inflicts 1d6+3 points of fire damage. Your bombs also inflict an additional 4d6 points of fire damage that is not multiplied on a critical hit or by using feats such as Vital Strike. Splash damage from an your bomb is always equal to the bomb's minimum damage (8). Those caught in the splash damage can attempt a DC 17 Reflex save for half damage.
Boneshard Bomb* (Su) The alchemist’s bomb deals piercing damage instead of fire damage, and creatures that take a direct hit from a boneshard bomb must succeed at a Fortitude save or take 1d4 points of bleed damage in addition to normal damage. If a creature is killed by a boneshard bomb or the resulting bleed effect, its corpse immediately reanimates as an undead creature with the skeleton template. Skeletons that are created in this manner count as undead created by animate dead for the purposes of determining how many undead the alchemist can control. An alchemist must possess the alchemical zombie discovery to select this discovery.
Confusion Bomb* (Su) Your bombs twist the target's perception of friend and foe. A creature that takes a direct hit from a confusion bomb takes damage from the bomb and is under the effect of a Confusion spell for 9 rounds. Reduce the amount of normal damage dealt by the bomb by 2d6 (so a bomb that would normally deal 6d6+4 points of damage deals 4d6+4 points of damage instead).
Precise Bombs Whenever the alchemist throws a bomb, he can select a number of squares equal to his Intelligence modifier that are not affected by the splash damage from his bombs. If the bomb misses, this discovery has no effect.
Smoke Bomb* When the alchemist creates a bomb, he can choose to have it create a cloud of thick smoke when it detonates. The cloud functions as fog cloud, filling an area equal to twice the bomb's splash radius for 1 round per level.
Stink Bomb* The effects of the smoke created by an alchemist's bomb can duplicate the effects of stinking cloud instead of fog cloud, filling an area equal to twice the bomb's splash radius for 1 round. An alchemist must possess the smoke bomb discovery before selecting this discovery.
Bonus Bombs (9x) Add +1/2 to the number of bombs per day the alchemist can create.
Brew Potion (Ex) You receive Brew Potion as a bonus feat. You can brew potions of any formulae you know (up to 3rd level), using your alchemist level as caster level. The spell must be one that can be made into a potion. You do not need to meet the prerequisites for this feat.
Fell Magic (Sp) +1 untyped bonus to DC to any Necromancy spells cast; If Wis 11+, SLAs: 1/day - Bleed, Chill Touch, Detect Poison, Touch of Fatigue. CL = Character Level. Save is Wis-based. [Cost: 3]
Hatred (Ex) Gnomes receive a +1 bonus on attack rolls against humanoid creatures of the reptilian and goblinoid subtypes due to special training against these hated foes.
Keen Senses (Ex) Gnomes receive a +2 bonus on Perception skill checks.
Knack With Poison Some gnomes have an instinctive understanding of poisons and their uses. Gnomes gain a +2 racial bonus on Fortitude saves against poison and a +2 bonus on Craft (alchemy) checks to make poison. The bonus on Fortitude saving throws against poisons increases to +4 if the gnome accidentally poisons himself when applying or readying the substance. This racial trait replaces illusion resistance and obsessive.
Low-Light Vision (Ex) You can see x2 as far as humans in low illumination. Characters with low-light vision have eyes that are so sensitive to light that they can see twice as far as normal in dim light. Low-Light Vision is color vision. A spellcaster with low-light vision can read a scroll as long as even the tiniest candle flame is next to her as a source of light. Characters with low-light vision can see outdoors on a moonlit night as well as they can during the day.
Mutagen (Su) You know how to create a mutagen that you can imbibe in order to heighten your physical prowess at the cost of your personality. It takes 1 hour to brew a dose of mutagen, and once brewed, it remains potent until used. You can only maintain one dose of mutagen at a time - if you brews a second dose, any existing mutagen becomes inert. A mutagen that is not in your possession becomes inert until an alchemist picks it up again. When you brew a mutagen, you select one physical ability score - either Strength, Dexterity, or Constitution. It's a standard action to drink a mutagen. Upon being imbibed, the mutagen causes you to grow bulkier and more bestial, granting you a +2 natural armor bonus and a +4 alchemical bonus to the selected ability score for 90 minutes. In addition, while the mutagen is in effect, you take a -2 penalty to one of your mental ability scores. If the mutagen enhances your Strength, it applies a penalty to your Intelligence. If it enhances your Dexterity, it applies a penalty to your Wisdom. If it enhances your Constitution, it applies a penalty to your Charisma. A non-alchemist who drinks a mutagen must make a DC 17 Fortitude save or become nauseated for 1 hour - a non-alchemist can never gain the benefit of a mutagen, but an alchemist can gain the effects of another alchemist's mutagen if he drinks it. (Although if the other alchemist creates a different mutagen, the effects of the "stolen" mutagen immediately cease.) The effects of a mutagen do not stack. Whenever an alchemist drinks a mutagen, the effects of any previous mutagen immediately end.
Poison Resistance (Ex) You gain a +6 bonus on all saving throws against poison.
Poison Use (Ex) You are trained in the use of poison and cannot accidentally poison yourself when applying poison to a weapon.
Swift Alchemy (Ex) You can create alchemical items with astounding speed. It takes you half the normal amount of time to create alchemical items, and you can apply poison to a weapon as a move action.
Swift Poisoning (Ex) You can apply a dose of poison to a weapon as a swift action.
Throw Anything (Ex) You gain the Throw Anything feat as a bonus feat. You add your Intelligence modifier to damage done with splash weapons, including the splash damage if any. This bonus damage is already included in the bomb class feature.
Weapon Familiarity (Ex) Gnomes treat any weapon with the word "gnome" in its name as a martial weapon.
The gnomes trust steed... errr, hill giant zombie.
Hill Giant Fast Zombie
NE Large undead
Init +0, Senses darkvision (60 ft.); Perception +0
=================================================
DEFENSE
=================================================
AC 16, touch 9, flat-footed 16 (+6 armor, +3 natural, -1 size )
hp 66 (12d8+12)
Fort +4, Ref +3, Will +4
Immunities undead traits
=================================================
OFFENSE
=================================================
Speed 35 ft.
Melee greatclub +15/+10 (2d8+10)
Melee slam +15/+15 (1d8+12)
Ranged rock +8/+3 (1d8+12)
Space 10 ft. Reach 10 ft.
=================================================
STATISTICS
=================================================
Str 27, Dex 10, Con -, Int -, Wis 10, Cha 10
Base Atk +8; CMB +17; CMD 27
Feats Martial Weapon Proficiency (greatclub), Toughness
Skills -
SQ quick strikes
Combat Gear
Other Gear greatclub, breastplate
=================================================
SPECIAL ABILITIES
=================================================
Quick Strikes (Ex) Whenever a fast zombie takes a full attack action, it can make one additional slam attack at its highest base attack bonus.