The 10th colossus (Dirge) looks the most snake-like, it chases and tries to eat the player during the fight. The 7th colossus Hydrus is based on an electric eel
One of the Colossi has what looks like teeth on top of its head, as if the top part of its skull is missing. This detail can be easy to miss on a first playthrough. The 'teeth' can be struck to move the Colossus around during the battle.
It is very easy to fall off of the colossi. Some are so large that this may result in Wander dying of fall damage.
*MAJOR SPOILER*
The main characters horse is believed to be dead after a bridge collapses whilst Wander is riding on Agro. Agro is revealed to be alive in the ending, but is injured and walks with a limp. This scene is very emotional.
One of the bosses must be shot in the eye to defeat it. There is no gore: the boss immediately closes its eyes and moves on to the next part of its battle.
The player character is shown being pierced by the souls of the colossi they slay. This looks like a possession however the player falls unconscious as a result and is transported back to the temple where they are given their next target.
Multiple of the arenas where you fight the colossi have the player entering building like structures where the player runs down dark corridors, down a slim staircase, or a low roofed building. People with severe claustrophobia may get overwhelmed, especially with the camera having issues in an enclosed space.
One of the characters uses plural pronouns ('we', 'us') when referring to themself, while another character uses masculine pronouns to refer to this character.
The 7th colossus Hydrus takes place in a lake, so general warning if you have thalassophobia. It dives underwater and can drag the player under with it