!ask how does priority during i.e showdown work? I play a reaction spell or unit. Do I still have focus to play another reaction speed unit or spell or does my opponent have it first? Alternatively after resolving the chain, who has priority to i.e open a new chain with an action speed spell?

Yes to reactions, no to focus. Playing a Reaction (or any chain item) gives you priority first, so you can stack multiple reactions in a row before your opponent gets a chance — focus isn't consumed by reactions (FAQ 4908, Rule 312.2.c/338.1.a.5). You only pass priority when you choose to pass it.

Once the chain empties back to a Showdown Open State, focus passes to the next player in turn order — that player gets priority and may open a new chain with an Action spell (Rule 340.2.a/346). You cannot "hold focus" to chain a second Action; you'd get focus back only after your opponent passes without acting (Rule 347).

One exception: if the chain opened from triggered abilities or an Add ability (e.g., the initial attack/defend trigger chain), focus does not pass when it closes — the attacker keeps it (Rule 346.1, FAQ 8169). Also remember: Actions can only be played during Open State; while the chain is up it's Reactions only.