The Lava Lotus makes its only appearance in SMB3 but it appears to have been based on the Panser from SMB2. (based on behavior and Japanese name) That might make it the only character from SMB2 to make it’s way into SMB3.
These aquatic plants let loose slow moving fireballs in regular patterns. Unlike their SMB2 days, these enemies are rooted in place and are non-aggressive. Unlike more underwater creatures, the Lava Lotus isn’t hurt by fire power, so you’ll have to just swim carefully by instead of attacking.