There are several versions of the card, each of which lets you choose from several unrelated effects, like flipping one of your opponent's cards over
At least you didn't plug Super Rejuv How would rejuv help here
Ok Seel #41 (Pokemon Base Set) Details All prices are the current market price
"Elemental HERO Shadow Mist" is a once-per-turn searcher for all "HERO" monsters when sent to the GY (usually by "Vision HERO Vyon"), but it is also a searcher for "Change" Spell Cards, which enables the Special Summon of the powerful "Masked HERO" monsters (most notably "Dark Law" and "Acid", the former can be Summoned using the wide pool of DARK "HERO" monsters available including "Shadow Mist" herself while the latter is Summoned by using "Absolute Zero" to perform a board wipe)
Considering Single Strike is a style based around big, expensive attacks, having that guaranteed energy each turn is incredibly useful
Red Card is an effective way to disrupt your opponent from setting up their board state