diff --git a/libmamba/data/mamba.xsh b/libmamba/data/mamba.xsh
index 31775802f6..cefacab6c0 100644
--- a/libmamba/data/mamba.xsh
+++ b/libmamba/data/mamba.xsh
@@ -20,7 +20,9 @@ _REACTIVATE_COMMANDS = ('install', 'update', 'upgrade', 'remove', 'uninstall')
 def _parse_args(args=None):
     from argparse import ArgumentParser
     p = ArgumentParser(add_help=False)
-    p.add_argument('command')
+    p.add_argument('command', nargs='?')
+    p.add_argument('-h', '--help', dest='help', action='store_true', default=False)
+    p.add_argument('-v', '--version', dest='version', action='store_true', default=False)
     ns, _ = p.parse_known_args(args)
     if ns.command == 'activate':
         p.add_argument('env_name_or_prefix', default='base')
@@ -44,9 +46,9 @@ def _raise_pipeline_error(pipeline):
 def _mamba_activate_handler(env_name_or_prefix=None):
     if env_name_or_prefix == 'base' or not env_name_or_prefix:
         env_name_or_prefix = $MAMBA_ROOT_PREFIX
-    __xonsh__.execer.exec($($MAMBA_EXE shell activate -s xonsh -p @(env_name_or_prefix)),
+    __xonsh__.execer.exec($($MAMBA_EXE shell activate -s xonsh @(env_name_or_prefix)),
                           glbs=__xonsh__.ctx,
-                          filename="$($MAMBA_EXE shell activate -s xonsh -p " + env_name_or_prefix + ")")
+                          filename="$($MAMBA_EXE shell activate -s xonsh " + env_name_or_prefix + ")")
 
 
 def _mamba_deactivate_handler():
@@ -91,6 +93,7 @@ if 'CONDA_SHLVL' not in ${...}:
 
 
 aliases['micromamba'] = _micromamba_main
+aliases['mamba'] = _micromamba_main
 
 
 @contextual_command_completer
diff --git a/libmamba/src/core/activation.cpp b/libmamba/src/core/activation.cpp
index da261b0926..9bd5a324f4 100644
--- a/libmamba/src/core/activation.cpp
+++ b/libmamba/src/core/activation.cpp
@@ -1123,7 +1123,7 @@ namespace mamba
 
         for (const std::string& uvar : env_transform.unset_vars)
         {
-            out << "del $" << uvar << "\n";
+            out << "try:\n  del $" << uvar << "\nexcept KeyError:\n  pass\n";
         }
 
         for (const auto& [skey, svar] : env_transform.set_vars)
diff --git a/micromamba/tests/test_activation.py b/micromamba/tests/test_activation.py
index acf1b50904..a3593b58d0 100644
--- a/micromamba/tests/test_activation.py
+++ b/micromamba/tests/test_activation.py
@@ -1,6 +1,7 @@
 import os
 import pathlib
 import platform
+import re
 import shutil
 import subprocess
 import tempfile
@@ -933,6 +934,67 @@ def test_activate_envs_dirs(
     assert any([env_name in p for p in dict_res.values()])
 
 
+@pytest.mark.skipif(
+    "xonsh" not in valid_interpreters,
+    reason="xonsh not available",
+)
+@pytest.mark.parametrize("alias", ["micromamba", "mamba"])
+def test_xonsh_help_and_version(tmp_home, tmp_root_prefix, tmp_path, alias):
+    umamba = helpers.get_umamba()
+
+    s = [f"{umamba} shell init -r {tmp_root_prefix} -s xonsh"]
+    call_interpreter(s, tmp_path, "xonsh")
+
+    def call(s):
+        return call_interpreter(s, tmp_path, "xonsh", interactive=True)
+
+    s = [f"{alias} --help"]
+    stdout, stderr = call(s)
+    assert not stderr, f"stderr was not empty: {stderr}"
+    assert "--help" in stdout
+    assert "Print this help message and exit" in stdout
+
+    s = [f"{alias} --version"]
+    stdout, stderr = call(s)
+    assert not stderr, f"stderr was not empty: {stderr}"
+    assert re.search(r"\d+\.\d+\.\d+", stdout.strip()), f"not a version: {stdout}"
+
+
+@pytest.mark.skipif(
+    "xonsh" not in valid_interpreters,
+    reason="xonsh not available",
+)
+@pytest.mark.parametrize("alias", ["micromamba", "mamba"])
+def test_xonsh_del_nonexistent_env_var(tmp_home, tmp_root_prefix, tmp_path, alias):
+    umamba = helpers.get_umamba()
+
+    s = [f"{umamba} shell init -r {tmp_root_prefix} -s xonsh"]
+    call_interpreter(s, tmp_path, "xonsh")
+
+    def call(s):
+        return call_interpreter(s, tmp_path, "xonsh", interactive=True)
+
+    helpers.create("-n", "test_unset_env", "--offline", "--no-rc", no_dry_run=True)
+
+    prefix = tmp_root_prefix / "envs" / "test_unset_env"
+    state_file = prefix / "conda-meta" / "state"
+    state_file.write_text(helpers.json.dumps({"env_vars": {"MAMBA_UNSET_TEST": "hello"}}))
+
+    # activate → manually delete var → deactivate
+    s = [
+        f"{alias} activate test_unset_env",
+        "del $MAMBA_UNSET_TEST",
+        f"{alias} deactivate",
+    ]
+
+    try:
+        stdout, stderr = call(s)
+    except subprocess.CalledProcessError:
+        pytest.fail("deactivate crashed on del of non-existent env var")
+
+    assert "does not contain any filesystem separator" not in stderr
+
+
 @pytest.fixture
 def tmp_umamba():
     mamba_exe = helpers.get_umamba()