They don't have to be the same creature both times, however
Junk Signal is best suited for a **Synchron / Yusei-style Synchro combo deck**, especially builds centered around **Junk Warrior, Stardust Dragon, and monsters that list them (like Junk Synchron, Stardust Synchron, or related support)**, because it both extends plays by tributing a monster to pull a key Synchro piece from hand, Deck, or GY and protects your Synchro effects from interruption
It's pretty hard to isolate all 1,694 Mystery Booster cards, especially since Scryfall now lumps them in with any other card printed from The List
Bosh and Slobad Bosh and Slobad are really interesting on this list because I'm not entirely sure I'd say they're terrible cards
So in a sense this card is narrow (dead vs control etc) but I wouldn't call it a sideboard card
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