Since the wererat uses a 1st-level warrior, lets just take the sample 1st-level halfling warrior from the MM...
Weremouse, Halfling Form
Small Humanoid (Halfling, Shapechanger)
Hit Dice: 1d8+1 plus 1d8 (9 hp)
Initiative: +1
Speed: 20 ft. (4 squares)
Armor Class: 18 (+1 size, +1 Dex, +2 natural, +3 studded leather, +1 light shield), touch 12, flat-footed 17
Base Attack/Grapple: +1/–3
Attack: Shortsword +4 melee (1d4/19–20) or light crossbow +3 ranged (1d6/19–20)
Full Attack: Shortsword +4 melee (1d4/19–20) or light crossbow +3 ranged (1d6/19–20)
Space/Reach: 5 ft./5 ft.
Special Attacks: Halfling traits
Special Qualities: Alternate form, halfling traits, mouse empathy, low-light vision, scent
Saves: Fort +6, Ref +4, Will +3
Abilities: Str 11, Dex 13, Con 12, Int 10, Wis 11, Cha 8
Skills: Balance +9, Climb +2, Hide +10, Jump +4, Listen +3, Move Silently +13, Swim +8
Feats: Stealthy, Weapon Finesse (B), Weapon Focus (shortsword)
Environment: Any
Organization: Solitary, pair, family (6–10), or troupe (2–5 plus 5–8 dire mice)
Challenge Rating: 2
Treasure: Standard
Alignment: Usually neutral
Advancement: By character class
Level Adjustment: +3
Weremouse, Mouse Form
Small Humanoid (Halfling, Shapechanger)
Hit Dice: 1d8+1 plus 1d8 (9 hp)
Initiative: +4
Speed: 40 ft. (8 squares), climb 20 ft.
Armor Class: 18 (+1 size, +4 Dex, +3 natural), touch 15, flat-footed 14
Base Attack/Grapple: +1/–5
Attack: Bite +4 melee (1d3-2)
Full Attack: Bite +4 melee (1d3-2)
Space/Reach: 5 ft./5 ft.
Special Attacks: Curse of lycanthropy
Special Qualities: Alternate form, damage reduction 10/silver, mouse empathy, low-light vision, scent
Saves: Fort +6, Ref +7, Will +3
Abilities: Str 7, Dex 19, Con 12, Int 10, Wis 11, Cha 8
Skills: Balance +12, Climb +14, Hide +13, Jump +18, Listen +3, Move Silently +16, Swim +12
Feats: Stealthy, Weapon Finesse (B), Weapon Focus (shortsword)
Environment: Any
Organization: Solitary, pair, family (6–10), or troupe (2–5 plus 5–8 dire mice)
Challenge Rating: 2
Treasure: Standard
Alignment: Usually neutral
Advancement: By character class
Level Adjustment: +3
Weremouse, Hybrid Form
Small Humanoid (Halfling, Shapechanger)
Hit Dice: 1d8+1 plus 1d8 (9 hp)
Initiative: +4
Speed: 20 ft. (4 squares)
Armor Class: 18 (+1 size, +4 Dex, +3 natural), touch 15, flat-footed 14
Base Attack/Grapple: +1/–7
Attack: Shortsword +7 melee (1d4-2/19–20) or claw +6 melee (1d3-2) or light crossbow +6 ranged (1d6/19–20)
Full Attack: Shortsword +7 melee (1d4-2/19–20) and bite +1 melee (1d4-2); or two claws +6 melee (1d3-2) and bite +1 melee (1d4-2); or light crossbow +6 ranged (1d6/19–20)
Space/Reach: 5 ft./5 ft.
Special Attacks: Curse of lycanthropy
Special Qualities: Alternate form, damage reduction 10/silver, mouse empathy, low-light vision, scent
Saves: Fort +6, Ref +7, Will +3
Abilities: Str 7, Dex 19, Con 12, Int 10, Wis 11, Cha 8
Skills: Balance +12, Climb +6, Hide +13, Jump +8, Listen +3, Move Silently +16, Swim +12
Feats: Stealthy, Weapon Finesse (B), Weapon Focus (shortsword)
Environment: Any
Organization: Solitary, pair, family (6–10), or troupe (2–5 plus 5–8 dire mice)
Challenge Rating: 2
Treasure: Standard
Alignment: Usually neutral
Advancement: By character class
Level Adjustment: +3
Alternate Form (Su): A weremouse can assume a bipedal hybrid form or the form of a dire mouse.
Curse of Lycanthropy (Su): Any humanoid or giant hit by a weremouse's bite attack in animal or hybrid form must succeed on a DC 15 Fortitude save or contract lycanthropy.
Mouse Empathy (Ex): Communicate with mice and dire mice, and +4 racial bonus on Charisma-based checks against mice and dire mice.
Skills: A weremouse in any form has a +4 racial bonus on Hide checks and a +8 racial bonus on Balance, Jump, Move Silently, and Swim checks. A weremouse in rat or hybrid form uses its Dexterity modifier for Climb, Jump, and Swim checks. In mouse form, it has a +8 racial bonus on Climb checks and can always choose to take 10 on a Climb check, even if rushed or threatened.
Feats: Weremice gain Weapon Finesse as a bonus feat.
The weremouse presented here is based on a 1st-level halfling warrior who is a natural lycanthrope, using the following base ability scores: Str 11, Dex 13, Con 12, Int 10, Wis 9, Cha 8.