Soul Bubble
A Soul Bubble is a stronger relative of the Love Bubble enountered in Mario & Luigi: Partners in Time. The four Mario Bros. fought these while storming Shroob Castle, the Peach's Castle of the past after it was taken over by the Shroobs. A Soul Bubble is similar in appearance to a love bubble, except its body is cream-colored, and its X-ed out eyes are green.
Soul Bubbles have all the same attacks as Love Bubbles, except they attack much faster, making the attacks harder to dodge. Also, while the Love Bubble always circles the brothers a set number of times during its homing attack, the Soul Bubble's amount before attacking varies.
The most predominating difference between Soul Bubbles and Love Bubbles is that in addition to healing enemies, Soul Bubbles have the added ability to resurrect defeated enemies. The resurrected foes then get a free turn, so Soul Bubbles should be taken out first to avoid this.