Electro Goolix
The Electro Goolix first appeared in Pikmin:The After Years. It is a mildly tough enemy because of is ability to instantly kill every Pikmin except for Yellow Pikmin, which will drown instead. Because, as can be seen in the picture, there is still a gelatinous membrane, which will still drown any non-blue pikmin (unless they get electrocuted first).
How to Kill
The only way to kill this enemy is to continuously toss pikmin on its large nucleus: use Yellow Pikmin if you want to minimize pikmin deaths, Purple Pikmin if you do not have good aim, or any other color if you feel like being a psychopathic pikmin killer.
After Years
In Pikmin:The After Years, it is a recurring boss/enemy.