All 7 Combos with Omen Machine

Lavinia, Azorius Renegade + Omen Machine

Lock: All spells opponents cast using Omen Machine are countered, Players can't draw cards, Lock

At the beginning of each draw step, Omen Machine prevents the active player from drawing a card, and causes them to exile the top card of their library, and cast that card if its a spell without paying its mana cost, or put it onto the battlefield if it's a land. If an opponent casts a spell this way, Lavinia triggers, countering that spell.

Cards: Lavinia, Azorius Renegade, Omen Machine

Omen Machine + Drannith Magistrate

Lock: Opponents can only cast the remaining spells in their hand, Lock