Viewing Design Quirks
Design Quirk Information
General Details
Name:  Prototype
Type:     Negative
Cost:  Two (2)
Available To:  BattleMechs
Reference:  BattleMech Manual (p. 88)

Description:
The ’Mech is a prototype and still has some issues. Its systems are less resilient and lack the redundancy that will be incorporated into the production model. All rolls for critical damage are modified by +2, making critical hits much more likely. Results of 13 or over are treated as 12 (except if using Advanced Determining Critical Hits, in which case do not modify down).

Even if brand new, designs that have just entered service have all passed the prototype stage and so likely do not qualify for this quirk. ’Mechs found in the Experimental Technical Readout series of products would make good candidates.