The verbal stem –essō (rarely -issō) may be grafted onto existing verbs to denote a certain energy or eagerness of action (though not necessarily repetition.)
Capiō (take) —> capessō (snatch)
Faciō (do) —> facessō (do eagerly)
Petō (seek) —> petissō (look frantically for)
Declension of such verbs is usually third declension for present and infinitive, but fourth declension for perfect and supine.
Capessō, capessere, capessīvī, capessītum
Petissō, petissere, petissīvī, petissītum
This is somehow related to the rare variant of the future perfect stem -āssō.
amāssis (for ameris)
although these forms are so rare that there’s no complete declension of any one verb in this form in all extant Latin literature, fragmentary appearances suggest that these too would follow the third (present, infinitive) / fourth (perfect, supine) pattern
Compounds of faciō vary between passives in -fīō and passives in -ficior. The distinction? Check the vowel a (faciō) in the compound. In the rare case that this is retain in the compound, then –fīō is also retained.
benefaciō, benefacere, benefēcī, benefactum (in place of the expected beneficio/ficere/fēcī/fectum, and hence the English ‘benefaction’ but also ‘infection.’)
benefīō, benefierī, benefactus sum
Several of the faciō compounds that feature -ficiō/-ficior forms will also feature passive -fīō forms, with separate meanings.