The aim of this paper is to show the full range of possible participant-function mappings available for the classes of verbs in Polish which denote predicates entailing an 'intermediary agent'. An intermediary agent is a semantic participant that can be conceptualised as an instrument or means with which the event is accomplished, or alternatively as the causer or instigator of this event. The particular verb classes involved include verbs of emission of smell, sound, or light, verbs expressing expansion of an aggregate or a mass/abstract entity (corresponding roughly to the English SWARM verbs), and verbs expressing physical or psychological states due to a stimulus which can be interpreted as an intermediary agent. I discuss how to model the identified alternations with LMT and offer argument structure models of all the variants. I argue that a certain type of clause which is often regarded as impersonal (due to the lack of a lexically expressed nominative subject, as well as the defocusing of the instigator) can be analysed as having a 'pro-drop' subject (an unexpressed/incorporated pronoun or pronominal inflection) which may co-refer with an overtly expressed instrument or other oblique argument.