The 3rd Level or Platform contains the Palace of the Frets, also called the Palace of the Grecas and War.  I do not recall much more about this level.  The symbol on the Palace of the Frets reminded me of the Mayan Tzolkin symbol.

According to the LONELY PLANET: Guide to Mexico, 9th Edition,  (2004), ISBN 1-74059-686-2, page 811, the Palace of the Grecas and War contains zigzag “X” shapes (Grecas), possibly representing Quetzalcoatl.  To the right of this Palace is a rambling series of chambers, passages, and stairways that archaeologists believe was Tonina’s administrative headquarters.  Near the middle of this level is a tomb with a stone sarcophagus.

According to MAYAS and ZOCQUES Southeastern Mexico: Chiapas, ISBN 798-970-678-031-7, Page 44, (Laura Pescador Canton author), stepped frets became a predominant decorative feature in much of Mesoamerican architecture at the end of the Classic Period.  The fretwork on this palace is the largest arrayed on the face of a wall, measuring 7 meters (23 feet) high by 21 meters (69 feet) wide.  Archaeologists believe that this “X” symbol represents the Sacred Mountain, the 3 cosmic levels in Mayan Spiritual thought (I know, does not agree with LONELY PLANET).  The Palace has 2 levels, with a central staircase connecting them that starts at the 3rd platform and ends at a throne made of stone and covered with stucco.  The Mayans decorated the throne with the symbol for Venus and bordered it with simulations of precious stones.  The throne is a tripod, with an Ahau glyph decorating each leg.  Along the lower part, a motif of bundles of arrows and shields resting on a jaguar skin adorns a fillet.