In an era where rapid, accurate keyboarding underpins virtually every academic, professional and everyday digital interaction, conventional drill-based tutors still struggle to sustain user engagement and to adapt difficulty in real time. Addressing this gap, we present Terra INVicta, a browser-native serious game that defends Earth from procedurally generated “cosmic” threats only when the player types their associated words correctly, thereby combining cognitive processing and motor skills practice in an engaging and accessible way. This paper details the game’s design workflow and a first-round evaluation of its gameplay mechanics and adaptive-difficulty engine, which modulates challenge through a mixed time–score progression factor. Initial tests indicate that Terra INVicta delivers fluid animation, near-instant keystroke-to-action responsiveness, and sustains a “flow” state across diverse player abilities, confirming its viability as a cognitive training game. Beyond validating its educational value, we highlight lessons learned and propose future work—including their application as a tool for cognitive assessment and improvement of cognitive and motor-skills in older adults. An interactive prototype is available at https://inverosimilitudes.github.io/TerraINVicta/ .