<p>All tonally derived verbs in Mwaghavul have ideophonic bases and are derived through one of two lexically determined alternations. In the first alternation, every tone-bearing unit (TBU) of the ideophone surfaces with a mid tone. In the second alternation, every nonfinal TBU of ideophones surfaces with a mid tone, while the final TBU surfaces with a high tone. To express pluractionality, both types of ideophones are reduplicated and follow the second pattern: every TBU of the reduplicant bears a mid tone, and every TBU of the base bears a high tone. While verbs derived through mid-tone overwrite share a tonal melody with underived verbs, only derived verbs have a mid–high melody. Beyond verb formation, the tonal alternations introduce various meanings, conveying the distinguishability of identical elements. We propose that the alternations are triggered by lexically specific allomorphs of a verbaliser, whose exponents are mid and mid–high tonal melodies, respectively. The restriction of the mid–high melody to derived verbs reflects systematicity. For the derived pluractional verbs, the tonal dissimilarity between a reduplicant and its base depicts the distinguishability of otherwise identical elements. We consider the implications of the patterns for linguistic theory, particularly the relationship between grammatical integration and expressiveness.</p>