Semi-major axis (left) and mass (right) evolution from multi-protoplanet growth. The planet and disk parameters are: M_p0 = 0.01 M_⊕, α_t = 5 × 10⁻³, M_d = 0.15 M_★, ξ_p/g = 1.75% and t_disk = 3.7 Myr. The filled dots indicate the planet-planet collisions. The transition radius is illustrated in the dashed line in the left panel, while the dot-dashed lines in the right panel represent the pebble isolation mass at the transition radius. By a combination of pebble accretion and planet-planet collisions, a system with one gas giant and three super-Earths form in very-low-mass stars of M_★ = 0.1 M_⊙.