The question already deals with possible answers. However, terminal velocity is more affected by air density than acceleration due to the reduced gravity. Expect terminal velocity to be fairly low. Drag forces increase proportionally to the mass density of air. The terminal velocity for a falling human, on Earth, is approximately 120 miles per hour. On your planet this would be reduced to about ten miles per hour.
Evolution would favour flight, so flying and gliding organisms will be in abundance. This could include creatures that simply fall as terminal velocity would be so low.
Slower rates of falling could result in slower reflexes and neural speeds. Creatures wouldn't need to correct so rapidly to falling so they would react in what would appear to be slower motion (not slow motion as seen on film or TV). They only need to act, react and save themselves more slowly than high-gravity creatures like humans from Earth.
Hopping and jumping forms of locomotion would appear to have an advantage in low gravity of 0.5 g, but the denser atmosphere would be an impediment. However, this is an impediment that lifeforms could take advantage of, by short-rang gliding.
Normally gliding animals drop from trees to gain the speed they need to glide. On a low gravity, high atmospheric density planet, gliding speed might be achieved at ground level enabling creatures to travel in short, low bursts. This might consist of a kangaroo-like jump, spreading its glider possum-like wings and gliding further than the jump normally allow.
Hexapods might be more probable on high-gravity planets. They are more likely the result of benthic lifeforms (ones that live sea bottoms). On Earth, most land animals are tetrapods because our remote ancestor was a teleost fish and its four fins eventually became our four limbs.
Whether low gravity planets have their animal life as tetrapods or hexapods depends on the quirkiness of the planet's evolutionary history independently of its gravity.
EDIT:
Almost so obvious it's easy to forget. The wind on a planet with twelve-times air density will be an exceptionally powerful force. This makes the possibility of wind-born lifeforms a high probability. On Earth there are many seeds and spores that are wind-borne. Even spiders, particularly social spiders, can create masses of web that can be carried on the wind.
Recently in Australia there were outbreaks of the Russian wheat aphid that had arrived from South Africa and carried by wind.
High-density winds will make wind-surfing lifeforms effectively a certainty. Compared to wind-borne organisms on Earth on your hypothetical plabet they will be reasonably large.