CROSS-PACK GAMEPLAY (WIP)
Build Buy
City Living - Original x Retro Gaming Console?
They are different and only one can be connected to each TV at a time (the first one placed will connect). The Retro Console only has the two games shown in the screenshots/trailers (a RAMPAGE clone called TANTRUM and a Pokémon-like Voidcritters game), unless others unlock with the Video Gaming Skill. Both can be played single or multi-player, but neither has online play options, which makes sense for a dated device). It is the cheapest console at only 300 Simoleons.
Eco Lifestyle - Bug Farm?
Compatible with the Entomology Skill.
Get Together - Jumping Platform?
Compatible with the Diving Skill.
Island Living/Adventure Awaits - Water Vehicle Docks & Open Water Ladders?
You can use all both in both worlds on Waterfront Lots, but neither gives Diving Skill when diving off of docks.
Lovestuck - Free Weights?
Just décor still, sorry.
Seasons - Bee Box?
Compatible with the Entomology Skill.
Systems
Basegame/Pack - Events on Getaways?
Not completely sure. I think you can, but only the un-goaled version. I planned a MWS Wedding Event at the Von Haunt Estate in testing. Though I was allowed to set the Traditions, once the event started it removed them and ran as an un-goaled event.
Seasons - Holidays during Getways?
Not sure on this one. They seem to start and run fine if you are currently on a Getaway. Starting a new Getaway will end them early though, at least in the once case I've had this happen so far.
Miscellaneous
Outdoor Retreat - Insects?
Untested so far.