The Water Lily Jaguar

In the middle of this rollout image is the Water Lily Jaguar. It is on a witz (a living mountain) in between a wahy on the left and Chaak on the right. (There's also a serpent that is coming out of the witz.) The vessel was made between 600s AD and 700s AD, either in Mexico or Guatemala. From the Metropolitan Museum of Art. 

Known today as the Water Lily Jaguar, this underworld (or Xibalbá) god was one of the more major ones the ancient Maya worshiped. It was associated with royalty and libation (pouring liquid as a sacrifice.) The Water Lily Jaguar is still a puzzle for archaeologists, and there are different theories about what the ancient Maya believed about it.

Appearance

This vessel was made between the 600s AD to the
700s AD, in Guatemala. It's style is the Chamá style.
From the Metropolitan Museum of Art.

The Water Lily Jaguar looks like a jaguar that has water lilies on it or next to it and a collar of eyeballs, which could mean the god was connected to sacrifice.

As for the water lilies' placement, sometimes they're on the god, sometimes there's just one flower on its head (and its ears are water lily leaves,) and sometimes they're around it. (One description -- in a paper by J. Andrew McDonald and Brian Stross -- also says that you can find images of the god with a water lily "blade" is on its head, instead of a water lily flower.)

When the flowers are around or all over the Water Lily Jaguar, there are also symbols for Venus, but not just any Venus symbols. These were drawn so they look kind of like water lilies.

There's another notable feature of the Water Lily Jaguar: its teeth. The ancient Maya drew supernatural jaguars' teeth two ways. One way was to draw a fang in the middle of the mouth. The other way was to draw them with a tooth shaped like an ik' sign. But not the Water Lily Jaguar -- the ancient Maya drew it with regular canines.

Connection with Royalty
It looks like the ancient Maya believed the Water Lily Jaguar protected royalty. Another theory about this god's connection to royalty says it might have been a god of male lines of royalty. (Speaking of royalty, there's a burial at Tikal called Burial 196 that had a jade figurine of the Water Lily Jaguar  -- it weighs 3.5 pounds!)

Connection with Libation
Images of elites making libations show them with certain features. One feature is that the elites wear water lilies in their hair. The second feature is that they have jaguar spots on their skin.

Other Connections
One theory about the Water Lily Jaguar says that the god may have been connected to the rainy season. (Because water lilies bloom in the rainy season.) Another theory says that it was a god of plants as well as fertility. Meanwhile, the same theory that suggests the Water Lily Jaguar was a god of male lines of royalty also suggests that it was connected to fire.

References:
Google Books: "Mortuary Landscapes of the Classic Maya: Rituals of the Body and Soul"; Andrew K. Scherer; 2015

San Francisco State University: Mark C. Griffin Associate Professor, Department of Anthropology San Francisco State University: "Jaguar Manifestation in Mesoamerica and Peru"; Amandine Dorian Castex; August 2014

Journal of Ethnobiology": "Water Lily and Cosmic Serpent: Equivalent Conduits of the Maya Spirit Realm"; J. Andrew McDonald, Brian Stross; Spring/Summer 2012

Britannica: Libation

The Metropolitan Museum of Art: Vessel, Mythological Scene

The Metropolitan Museum of Art: Vessel, Throne Scene

Image Credit:
The Metropolitan Museum of Art: Vessel, Mythological Scene (Second additional image)

The Metropolitan Museum of Art: Vessel, Throne Scene (Fourth additional image)