Sailor Plank

Players of Super Mario Advance may recall that one of the major changes in that game compared to the Super Mario All-Stars version of Super Mario Bros. 2 (on which it is mostly based) is the inclusion of two new boss intros for Fryguy and Clawgrip, respectively.

In both cases, the action stops and a cutscene shows four bubbles (identical to Wart's bubble attack) float up from the bottom of the screen and surround an entity before transforming it into the boss (a mask for Fryguy and a small Sidestepper crab for Clawgrip).

The game actually contains two unused scenes for the same intro happening with two more bosses: Mouser and Tryclyde, shown restored in the footage. Mouser is created from a unique small mouse sprite, while Tryclyde is created from a Cobrat.

This implies that during the game's development the idea of Wart's magic being responsible for most of the game's bosses was more prevalent, before these scenes were scrapped for an unknown reason.

Source: AkiraTheGamer