The TremorPak was Performance/InterAct's version of Nintendo's Rumble Pak. Across it's numerous iterations, it included a vibration speed switch, featuring high and low (power-saving) modes.
Many budget third-party manufacturers during this era sold products where the image on the box did not match the product inside the box. At least one example of this variant containing the original wedge-shaped TremorPak insider the "Nintendo Style" box has been found.
Trivia
In 1999, Performance released a variation of their TremorPak that changed visually from their earlier releases. Instead of the wedge shape at one end, Performance redesigned it to look more similar to Nintendo's rumble pack; this variant is much more square.