How can I create different portals to different sky block islands for multiplayer?

Best Solution

From they way you posed the question it sounded like you intended to use minecraft's built-in portals, particularly the nether portal, impossible to do without a mod or script. (which you should provide more information about)

However the best, most well rounded solution I can come up with is a teleportation pad using a "special" block. The command for that would look something like this.

The command:

execute at @e[distance=..3] if block ~ ~-1 ~ ^your block^ at @s as @s run tp @e[distance=..3,limit=1] ^coordinates^ ^rotational coordinates^

• ^your block^ is where players(and all entities including items and pantings) are teleported from, it should never show up anywhere else in the map.
• ^coordinates^ where you want to teleport to. Your current coordinates (x, y, z) can be found by pressing Fn+F3 and looking for Block: "some numbers/coordinates".
• ^rotational coordinates^ these are 2 more coordinates that determine the direction your looking, these can be found by looking 2 rows under your coordinates.
  
  By placing this command in a "repeating" command block set to "always active" right next to or under ^your block^, players will be teleported to ^coordinates^. From the side would look like...

---

• □=Air
• ▅=Block
• ▣=Command Block
• ⊞=Portal Stone
  
  ▅ ▅ ⊞ ⊞ ⊞ ▅ ▅
  ▅ ▅ ▅ ▣ ▅ ▅ ▅
  
  Or like this..
  
  □ □ □ □ □ □ ▣ □
  ▅ ▅ ⊞ ⊞ ⊞ ▅ ▅
  
  Or this..
  
  ▅ ▅ ⊞ ⊞ ⊞ ▣ ▅
  ▅ ▅ ▅ ▅ ▅ ▅ ▅
  
  

---

To add some flare to the teleport, add a similar command block with an identical command but instead of run tp type run particle. For the sake of being concise, I will link to another forum post that explains how to finish the command.

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