How are Far Cry 3 and Far Cry 3: Blood Dragon related

Solution 1:

The gameplay of Blood Dragon is largely based on Far Cry 3. Most of the enemies are identical to FC3, except for their graphics. The terrain is also very similar to FC3.

Many unique gameplay aspects from Far Cry 3 were used with almost no modifications:

• Open-World gameplay with a world map
• Collectibles
• The cover mechanics
• The takedown mechanics
• The health mechanics
• Tagging enemies so you can see them through walls (now it at least makes sense)
• Behavior of human and animal opponents
• Experience point mechanic which rewards you for complicated kills (although the scoring was changed to encourage a more aggressive playstyle)
• Buying weapon attachments
• Conquering of enemy outposts to reduce enemy patrols and unlock sidequests
• Vehicle physics, including the hang glider

Notable FC3 features which were dropped are:

• Unlocking of items and maps by radio towers
• Obtaining weapons by buying them or picking them up - all weapons are now found during the story missions
• Skill tree (each levelup now gives you a specific skill)
• Item Crafting
• Minigames like poker, knive throwing etc.
• Day/night cycle (it's always night)

Notable new features are:

• Completely unrelated story with new characters and voice acting
• The blood dragon enemies
• Most of the weapons and their (quite powerful) addons
• Video cutscenes which do not use the game engine
• Completely new soundtrack

While the overall gameplay feels very similar to FC3, the whole atmosphere and the tone is completely different. While FC3 has a very serious tone with a dark and tragic storyline, Blood Dragon is a lot more light-hearted. It has a completely ridiculous plot with over-the-top characters, is ripe with parodies of movie-cliches of the 80s and game cliches of the 2000s and doesn't take itself one bit serious.

Or in different words: FC3 portraits the serious kind of insanity, FC3:BD portraits the funny kind of insanity.

Solution 2:

Blood Dragon is a totally new game built using the engine and assets of Far Cry 3. Think of it as an officially sanctioned Total Conversion mod that has been released as a standalone game.

Solution 3:

Their stories have nothing to do with each other, so they're not really related in that aspect. In FC3: Blood Dragon, some of the characters have comments that may be seen as a nod or a quip related to Far Cry 3. A similarity could be that they both take place in an island.

I've played both and noticed that most of the assets (the island details, textures, weapons, vehicles, animals, enemies, etc.) and most of the gameplay elements (outpost taking, skills, etc.) in FC3: Blood Dragon are just re-skinned or slightly modified versions of their counterparts in Far Cry 3.

Notable differences of FC3: Blood Dragon from Far Cry 3 include: the Blood Dragon creature, which doesn't have a counterpart in Far Cry 3, and that tediously climbing radio towers is not a significant part of the gameplay anymore.