Merge takes two ideas and stacks them. The outer surface is a wide rubber flat, and pushing up through the middle of it is a small plastic sharp. Which one contacts the floor depends entirely on attitude: launched clean and level, the bey rides the plastic sharp, sits near the centre and behaves like a stamina part, but knocked off axis — or launched at a deliberate angle — the rubber ring bites the floor and the combo turns aggressive. Merge also runs eighteen gears, more than any bit before it, which makes an Xtreme Dash noticeably faster.
The costs are real. Rubber and eighteen gears both drain spin, so Merge does not win stamina exchanges outright; it wins by dictating which mode it fights in. It is also the tallest bit released and among the heaviest, which changes the whole combo’s centre of gravity.
Because of that height, Merge wants short ratchets to keep the build from sitting absurdly tall. Players who only want the aggressive half of its behaviour take a dedicated attack bit instead; those who only want the passive half take a plain sharp or Ball. It is recent enough that no settled competitive verdict exists.