Hesitated to post my designs for this one because I think I may be cheating. My 'killer' comes with two slight variants, Master:
Ballista BLL-1CM
Mass: 60 tons
Tech Base: Inner Sphere
Chassis Config: Biped
Rules Level: Tournament Legal
Era: Clan Invasion
Tech Rating/Era Availability: E/X-X-E-A
Production Year: 3060
Cost: 11,709,760 C-Bills
Battle Value: 1,255
Chassis: Unknown Endo-Steel
Power Plant: Unknown 300 Light Fusion Engine
Walking Speed: 54.0 km/h
Maximum Speed: 86.4 km/h
Jump Jets: Unknown
Jump Capacity: 90 meters
Armor: Unknown Standard Armor w/ CASE
Armament:
2 MML-9s
1 Medium Laser
1 C3 Computer (Master)
Manufacturer: Unknown
Primary Factory: Unknown
Communications System: Unknown
Targeting and Tracking System: Unknown
================================================================================
Equipment Type Rating Mass
--------------------------------------------------------------------------------
Internal Structure: Endo-Steel 99 points 3.00
Internal Locations: 4 LT, 3 LA, 3 RA, 2 LL, 2 RL
Engine: Light Fusion Engine 300 14.50
Walking MP: 5
Running MP: 8
Jumping MP: 3 Standard
Jump Jet Locations: 1 CT, 1 LT, 1 RT 3.00
Heat Sinks: Double Heat Sink 10(20) 0.00
Gyro: Standard 3.00
Cockpit: Standard 3.00
Actuators: L: SH+UA+LA+H R: SH+UA+LA+H
Armor: Standard Armor AV - 168 10.50
CASE Locations: 1 LT, 1 RT 1.00
Internal Armor
Structure Factor
Head 3 9
Center Torso 20 27
Center Torso (rear) 6
L/R Torso 14 21
L/R Torso (rear) 5
L/R Arm 10 16
L/R Leg 14 21
================================================================================
Equipment Location Heat Critical Mass
--------------------------------------------------------------------------------
Medium Laser CT 3 1 1.00
C3 Computer (Master) RT 0 5 5.00
MML-9 RA 5 5 6.00
MML-9 LA 5 5 6.00
@MML-9 (LRM Narc) (13) RT - 1 1.00
@MML-9 (SRM Narc) (11) RT - 1 1.00
@MML-9 (LRM Narc) (13) LT - 1 1.00
@MML-9 (SRM Narc) (11) LT - 1 1.00
Free Critical Slots: 4
BattleForce Statistics
MV S (+0) M (+2) L (+4) E (+6) Wt. Ov Armor: 6 Points: 13
5/2j 3 2 1 0 3 0 Structure: 3
Special Abilities: C3M, TAG, CASE, MHQ5, SRCH, ES, SEAL, SOA, IF 1
And Slave, which trades the C3M and medium laser for C3S and an LRM10, adjusting the ammo to fit:
Ballista BLL-1CS
Mass: 60 tons
Tech Base: Inner Sphere
Chassis Config: Biped
Rules Level: Tournament Legal
Era: Clan Invasion
Tech Rating/Era Availability: E/X-X-E-A
Production Year: 3060
Cost: 9,805,760 C-Bills
Battle Value: 1,326
Chassis: Unknown Endo-Steel
Power Plant: Unknown 300 Light Fusion Engine
Walking Speed: 54.0 km/h
Maximum Speed: 86.4 km/h
Jump Jets: Unknown
Jump Capacity: 90 meters
Armor: Unknown Standard Armor w/ CASE
Armament:
1 LRM-10
2 MML-9s
1 C3 Computer (Slave)
Manufacturer: Unknown
Primary Factory: Unknown
Communications System: Unknown
Targeting and Tracking System: Unknown
================================================================================
Equipment Type Rating Mass
--------------------------------------------------------------------------------
Internal Structure: Endo-Steel 99 points 3.00
Internal Locations: 4 LT, 3 LA, 3 RA, 2 LL, 2 RL
Engine: Light Fusion Engine 300 14.50
Walking MP: 5
Running MP: 8
Jumping MP: 3 Standard
Jump Jet Locations: 1 CT, 1 LT, 1 RT 3.00
Heat Sinks: Double Heat Sink 10(20) 0.00
Gyro: Standard 3.00
Cockpit: Standard 3.00
Actuators: L: SH+UA+LA+H R: SH+UA+LA+H
Armor: Standard Armor AV - 168 10.50
CASE Locations: 1 LT, 1 RT 1.00
Internal Armor
Structure Factor
Head 3 9
Center Torso 20 27
Center Torso (rear) 6
L/R Torso 14 21
L/R Torso (rear) 5
L/R Arm 10 16
L/R Leg 14 21
================================================================================
Equipment Location Heat Critical Mass
--------------------------------------------------------------------------------
C3 Computer (Slave) CT 0 1 1.00
LRM-10 RT 4 2 5.00
MML-9 RA 5 5 6.00
MML-9 LA 5 5 6.00
@MML-9 (LRM Narc) (13) RT - 1 1.00
@LRM-10 (Narc) (12) RT - 1 1.00
@MML-9 (LRM Narc) (13) LT - 1 1.00
@MML-9 (SRM Narc) (11) LT - 1 1.00
Free Critical Slots: 7
BattleForce Statistics
MV S (+0) M (+2) L (+4) E (+6) Wt. Ov Armor: 6 Points: 13
5/2j 3 3 2 0 3 0 Structure: 3
Special Abilities: C3S, CASE, MHQ1, SRCH, ES, SEAL, SOA, LRM 0/1/2, IF 2
While you did say C3 was encouraged I'm not sure this is what you intended. Here's the 'hunter' to round things out:
Pointer POI-1R
Mass: 50 tons
Tech Base: Inner Sphere
Chassis Config: Biped
Rules Level: Tournament Legal
Era: Clan Invasion
Tech Rating/Era Availability: E/X-X-E-A
Production Year: 3060
Cost: 8,262,000 C-Bills
Battle Value: 1,173
Chassis: Unknown Standard
Power Plant: Unknown 300 Light Fusion Engine
Walking Speed: 64.8 km/h
Maximum Speed: 97.2 km/h
Jump Jets: Unknown
Jump Capacity: 180 meters
Armor: Unknown Standard Armor w/ CASE
Armament:
4 Medium Lasers
1 Narc Launcher
1 C3 Computer (Slave)
Manufacturer: Unknown
Primary Factory: Unknown
Communications System: Unknown
Targeting and Tracking System: Unknown
================================================================================
Equipment Type Rating Mass
--------------------------------------------------------------------------------
Internal Structure: Standard 83 points 5.00
Engine: Light Fusion Engine 300 14.50
Walking MP: 6
Running MP: 9
Jumping MP: 6 Standard
Jump Jet Locations: 3 LT, 3 RT 3.00
Heat Sinks: Double Heat Sink 10(20) 0.00
Gyro: Standard 3.00
Cockpit: Standard 3.00
Actuators: L: SH+UA+LA+H R: SH+UA+LA+H
Armor: Standard Armor AV - 160 10.00
CASE Locations: 1 RT 0.50
Internal Armor
Structure Factor
Head 3 9
Center Torso 16 25
Center Torso (rear) 6
L/R Torso 12 19
L/R Torso (rear) 5
L/R Arm 8 16
L/R Leg 12 20
================================================================================
Equipment Location Heat Critical Mass
--------------------------------------------------------------------------------
C3 Computer (Slave) HD 0 1 1.00
2 Medium Lasers CT 6 2 2.00
Narc Launcher RA 0 2 3.00
2 Medium Lasers LA 6 2 2.00
@Narc (Homing) (12) RT - 2 2.00
@Narc (Explosive) (6) RT - 1 1.00
Free Critical Slots: 26
BattleForce Statistics
MV S (+0) M (+2) L (+4) E (+6) Wt. Ov Armor: 5 Points: 12
6j 2 2 0 0 2 0 Structure: 3
Special Abilities: C3S, SNARC, CASE, MHQ1, SRCH, ES, SEAL, SOA