Let's break the horizontal progression with some goofy but useful stuff.
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The player ghost
You can sit down and then control your ghost. Can be used for scouting and talking with other players. The ghost can't use the normal player actions. While shooting yourself from a cannon you can summon the ghost to readjust the direction. -
Animal/pet possession
You can take control of an animal or pet and use them for scouting. The chickens and birds can fly at speed of Galleon with full wind. The monkeys, pigs and snakes can run/swim 33% faster than the flying. -
The voyage call
You have sixth sense when doing voyages. Holding the "X" marks the spot map would show a ghostly "X" at the spot. Holding the riddle would higlight the objective. Holding the skeleton map would show flying skeleton heads leading to the place where skeletons spawn. Holding the animal map would show you a spirit animal running to the closest real animal. Cargo runs would give you an indicator when the plants have to be watered, cloth could be dried a little, the bottles repaired slightly - you would also be able to protect the cargo in spiritual bubble when carrying it that blocks water while swimming, damage while jumping, plants from withering. -
The spirit tools
You can summon all kinds of tools.
a) Spirit stove - for cooking.
b) Spirit instrument - it plays the music and follows you so you can now play two instruments at once! Or use it while catching snakes.
c) Spirit lantern - flies around to give you light and the edge when fighting the shadow skeletons.
d) Spirit bucket - when the bucket is full it summons a rainy cloud that brings doom to the golden skeletons, can water plants and put down fires.
e) Spirit trumpet - are the plant skeletons standing in the rain? The spirit trumpet makes the air dry and so the skeletons.
f) Spirit tankard - nothing spiritual about it, you can just puke in an empty tankard and use it like the bucket.
g) Spirit watch - shows you time till the next island reset / reaper spawn.
h) Spirit compass - the compass is flying in front of you so you can do other things while knowing the direction.
e) Spirit spy glass - you can see players as spirits though objects so no more tucking.
f) Spirit shovel - a spiritually connected shovel that helps you to dig up chests at twice the speed.
g) Spirit fishing rod - you see which fish/object is gonna bite next.
And that's the end of the brainstorming for now.

