Good, Better, Best: Irregular Comparatives in Spanish

Spanish has a couple of adjectives and adverbs that are exceptions when it comes to forming the comparative and superlative.
As adjectives, bueno (good), malo (bad), grande (big), and pequeño (small) have irregular forms in the comparative and superlative. Note that grande and pequeño each have two different meanings in their comparative and superlative forms.
Irregular Adjectives in the Comparative and Superlative
Adjective                                                        Comparative                                                          Superlative
bueno (buena) (good)                                mejor (better)                                                          el/la mejor (the best)
buenos (buenas)                                         mejores                                                                       los/las mejores
malo (mala) (bad)                                      peor (worse)                                                              el/la peor (the worst)
malos (malas)                                             peores                                                                         los/las peores
grande (great, big)                                     mayor (older, greater in age or                              el/la mayor (the oldest,
status)                                                                           greatest)
más/menos grande (larger/less                               el más/menos grande
large in size)                                                                 (the largest/least large)

The adverbs bien (well) and mal (poorly) become mejor (better) and peor (worse), respectively, in their comparative forms and follow the verb or verb phrase they modify:
Tomás juega al fútbol mejor que Javier. (Thomas plays soccer better than Javier.)
Ella cocina peor que yo. (She cooks worse than I do.)