Slot 1: looping troop (chalcedony, beetrix, seekra, or others)
Slot 2: empowered converter (Empowered Troops Converter List)
Slot 3: other empowered troop (leprechaun or sister superior, etc.)
Slot 4: hero with weapon that uses mana colour created by looping troop and/or empowered converter.
Used in… Almost every event, especially guild war defence.
Examples of more specific teams.
Rope dart, forest guardian, quilin, moon rabbit. Reddit - Dive into anything
One I use often?
Norbert’s turnip, flaming oni, gobtruffle, stringfidler. Used in most event type, as long as restrictions allow. Needs a good board, but can easily cast all four spells MULTIPLE times within the first turn if it gets any troop’s mana filled from a four-gem-match or two.
Seriously, just pick four empowered troops and make them a team and it’d win battles against the first few enemy teams in most events. Sure, the potion isn’t needed in those first battles, but if your point is that you can’t make a team for the event that casts spells in the first turn, you absolutely can. And people do so, all the time.