diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ab0b95c87..e08aabe6c 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -42,6 +42,8 @@ Completions
   - ``otool``
   - ``pre-commit`` (:issue:`9521`)
   - ``proxychains`` (:issue:`9486`)
+  - ``mix phx``
+  - ``neovim``
 - Improvements to many completions.
 - git's completion for ``git-foo``-style commands was fixed (:issue:`9457`)
 - File completion now offers ``../`` and ``./`` again (:issue:`9477`)
diff --git a/share/completions/nvim.fish b/share/completions/nvim.fish
index fcb054f60..be8b27a70 100644
--- a/share/completions/nvim.fish
+++ b/share/completions/nvim.fish
@@ -1 +1,68 @@
-complete -c nvim -w vim
+type --quiet __fish_vim_tags || source (status dirname)/vim.fish
+
+# Options shared with vim, copied from vim.fish
+complete -c nvim -s c -r -d 'Execute Ex command after the first file has been read'
+complete -c nvim -s S -r -d 'Source file after the first file has been read'
+complete -c nvim -l cmd -r -d 'Execute Ex command before loading any vimrc'
+complete -c nvim -s i -r -d 'Set the shada file location'
+complete -c nvim -s o -d 'Open horizontally split windows for each file'
+complete -c nvim -o o2 -d 'Open two horizontally split windows' # actually -o[N]
+complete -c nvim -s O -d 'Open vertically split windows for each file'
+complete -c nvim -o O2 -d 'Open two vertically split windows' # actually -O[N]
+complete -c nvim -s p -d 'Open tab pages for each file'
+complete -c nvim -o p2 -d 'Open two tab pages' # actually -p[N]
+complete -c nvim -s q -r -d 'Start in quickFix mode'
+complete -c nvim -s r -r -d 'Use swap files for recovery'
+complete -c nvim -s t -xa '(__fish_vim_tags)' -d 'Set the cursor to tag'
+complete -c nvim -s u -r -d 'Use alternative vimrc'
+complete -c nvim -s w -r -d 'Record all typed characters'
+complete -c nvim -s W -r -d 'Record all typed characters (overwrite file)'
+complete -c nvim -s A -d 'Start in Arabic mode'
+complete -c nvim -s b -d 'Start in binary mode'
+complete -c nvim -s d -d 'Start in diff mode'
+complete -c nvim -s D -d 'Debugging mode'
+complete -c nvim -s e -d 'Start in Ex mode, execute stdin as Ex commands'
+complete -c nvim -s E -d 'Start in Ex mode, read stdin as text into buffer 1'
+complete -c nvim -s h -d 'Print help message and exit'
+complete -c nvim -s H -d 'Start in Hebrew mode'
+complete -c nvim -s L -d 'List swap files'
+complete -c nvim -s m -d 'Disable file modification'
+complete -c nvim -s M -d 'Disable buffer modification'
+complete -c nvim -s n -d 'Don\'t use swap files'
+complete -c nvim -s R -d 'Read-only mode'
+complete -c nvim -s r -d 'List swap files'
+complete -c nvim -s V -d 'Start in verbose mode'
+complete -c nvim -s h -l help -d 'Print help message and exit'
+complete -c nvim -l noplugin -d 'Skip loading plugins'
+complete -c nvim -s v -l version -d 'Print version information and exit'
+complete -c nvim -l clean -d 'Factory defaults: skip vimrc, plugins, shada'
+complete -c nvim -l startuptime -r -d 'Write startup timing messages to <file>'
+
+# Options exclusive to nvim, see https://neovim.io/doc/user/starting.html
+complete -c nvim -s l -r -d 'Execute Lua script'
+complete -c nvim -s ll -r -d 'Execute Lua script in uninitialized editor'
+complete -c nvim -s es -d 'Start in Ex script mode, execute stdin as Ex commands'
+complete -c nvim -s Es -d 'Start in Ex script mode, read stdin as text into buffer 1'
+complete -c nvim -s s -r -d 'Execute script file as normal-mode input'
+
+# Server and API options
+complete -c nvim -l api-info -d 'Write msgpack-encoded API metadata to stdout'
+complete -c nvim -l embed -d 'Use stdin/stdout as a msgpack-rpc channel'
+complete -c nvim -l headless -d "Don't start a user interface"
+complete -c nvim -l listen -r -d 'Serve RPC API from this address (e.g. 127.0.0.1:6000)'
+complete -c nvim -l server -r -d 'Specify RPC server to send commands to'
+
+# Client options
+complete -c nvim -l remote -d 'Edit files on nvim server specified with --server'
+complete -c nvim -l remote-expr -d 'Evaluate expr on nvim server specified with --server'
+complete -c nvim -l remote-send -d 'Send keys to nvim server specified with --server'
+complete -c nvim -l remote-silent -d 'Edit files on nvim server specified with --server'
+
+# Unimplemented client/server options
+# Support for these options is planned, but they are not implemented yet (February 2023).
+# nvim currently prints either a helpful error message or a confusing one ("Garbage after option argument: ...")
+# Once they are supported, we can add them back in - see https://neovim.io/doc/user/remote.html for their status.
+# complete -c nvim -l remote-wait -d 'Edit files on nvim server'
+# complete -c nvim -l remote-wait-silent -d 'Edit files on nvim server'
+# complete -c nvim -l serverlist -d 'List all nvim servers that can be found'
+# complete -c nvim -l servername -d 'Set server name'
diff --git a/share/completions/vim.fish b/share/completions/vim.fish
index 8f2426444..0a449e3cf 100644
--- a/share/completions/vim.fish
+++ b/share/completions/vim.fish
@@ -17,6 +17,7 @@ function __fish_vim_find_tags_path
     return 1
 end
 
+# NB: This function is also used by the nvim completions
 function __fish_vim_tags
     set -l token (commandline -ct)
     set -l tags_path (__fish_vim_find_tags_path)
@@ -40,9 +41,12 @@ complete -c vim -s S -r -d 'Source file after the first file has been read'
 complete -c vim -l cmd -r -d 'Execute Ex command before loading any vimrc'
 complete -c vim -s d -r -d 'Use device as terminal (Amiga only)'
 complete -c vim -s i -r -d 'Set the viminfo file location'
-complete -c vim -s o -r -d 'Open stacked windows for each file'
-complete -c vim -s O -r -d 'Open side by side windows for each file'
-complete -c vim -s p -r -d 'Open tab pages for each file'
+complete -c vim -s o -d 'Open horizontally split windows for each file'
+complete -c vim -o o2 -d 'Open two horizontally split windows' # actually -o[N]
+complete -c vim -s O -d 'Open vertically split windows for each file'
+complete -c nvim -o O2 -d 'Open two vertically split windows' # actually -O[N]
+complete -c vim -s p -d 'Open tab pages for each file'
+complete -c nvim -o p2 -d 'Open two tab pages' # actually -p[N]
 complete -c vim -s q -r -d 'Start in quickFix mode'
 complete -c vim -s r -r -d 'Use swap files for recovery'
 complete -c vim -s s -r -d 'Source and execute script file'
@@ -95,3 +99,5 @@ complete -c vim -l serverlist -d 'List all Vim servers that can be found'
 complete -c vim -l servername -d 'Set server name'
 complete -c vim -l version -d 'Print version information and exit'
 complete -c vim -l socketid -r -d 'Run gvim in another window (GTK GUI only)'
+complete -c vim -l clean -d 'Factory defaults: skip vimrc, plugins, viminfo'
+complete -c vim -l startuptime -r -d 'Write startup timing messages to <file>'