Any verb that undergoes a stem change in the present tense undergoes the same stem change in the present subjunctive in all forms except nosotros/nosotras and vosotros/vosotras. Only ‐ir verbs undergo a stem change in the nosotros/nosotras and vosotros/vosotras forms and, only in these forms, they undergo o> u or e> i stem changes. Notice that mostrar (Table ) and entender (Table ) do not undergo a stem change in the nosotros/nosotras and vosotros/vosotras forms, but dormir (Table ) does because it is an ‐ir verb.
The verb jugar (to play) is exceptionally tricky because it is a stem‐changer and also undergoes a spelling change. Because jugar is a very common verb, it is worth learning the forms in Table .