Harmonic Prodigy rewards decks built around Shamans and Wizards with an additional trigger whenever an eligible creature's triggered ability triggers. Its two-mana cost makes it easy to deploy before a more expensive engine, and prowess gives it a secondary role as an attacker in lists with plenty of noncreature spells. The main attraction, however, is how much extra work it lets your other creatures do.
Young Pyromancer is a Shaman, so its token-making trigger produces an additional trigger while Prodigy is on the battlefield. In blue-red decks, Niv-Mizzet, Parun benefits because it is a Wizard: its draw and damage triggers become much more productive. These pairings make Prodigy appealing in spellslinger strategies that build a board or draw through the library while casting interaction and cantrips.
Creature types deserve a careful check when selecting partners. The card does not double every trigger you control, and activated abilities are outside its scope. It also specifically excludes its own Wizard triggers, so its prowess ability does not receive an extra trigger from itself. A small number of excellent supported creatures is more valuable than assuming every spell payoff will qualify.
Try to cast Prodigy before the turn on which you expect several triggers, rather than exposing it unnecessarily while doing nothing else. Its modest body is easy to remove, but the low casting cost lets you combine it with a payoff or protective spell in the same turn.
