Ral Zarek might be good in a control deck but great in an aggressive deck, for instance
In Phyrexia: All Will Be One, Nahiri is one of the planeswalkers that succumbs to compleation, becoming nothing more than a tool in Phyrexias hands
The rest of the Side Deck is mostly focused on standard kinds of Side Deck cards from time that were targeted to stop decks that could flood the board with multiple Synchros, the main decks that did that being Blackwings and Synchro Cat
The biggest downside to this card is that you need to Tribute Summon it using five Monsters, which eats up resources and uses up your Normal Summon
In sets where there are more than one showcase, like Midnight Hunt, these will only be from one style, such as the Equinox frame
Themes: Horror tribal, milling opponents, and stealing their best creatures