This question asks about a specific symbol, which looks like a heart rate monitor. The monster icon and the heart rate below it are to the right of the minimap. On the minimap and the large map, if you can see the monster's icon, other symbols may appear, including:
- A flashing skull
- A monster head with drool running out its mouth
- A U- or eye-shaped icon that can be white, orange, or red (depicted on the minimap, as well as the ally's health in this picture)
- Green numbers with a plus-sign
- Red numbers with a minus-sign
I know the skull generally means "it's close to death, and probably capturable" and the drool probably means "it's hungry", but even then, I don't know all of the implications of these icons. An explanation of the above, and any others I may have missed, would be very appreciated.