Sentinels are invincible mechanized security droids that patrol looking for intruders. If caught in their tele-orb rays, Ninja is sent back to the last checkpoint, taking damage. To distract a Sentinel, throw a Shuriken or shoot a Dart, as this will make the Sentinel stop moving, but still uses tele-orb rays.
- In the Psyamon boss level, Ninja sees several two-legged walker machines that are very similar to the Sentinels (except with a different, camouflage-patterned paintjob and sporting pyro-storm miniguns with built-in power bolt launchers, instead of the Sentinels' quad-barreled weapon configuration) and actually pilots one of them in order to destroy the powerful demon. The machine's CPU identifies it as "The MK II Enforcer". Judging by its design and the emitter under the cockpit, it, like the Sentinels, is capable of shooting tele-orb rays (though Ninja never uses them, nor is the player able to in-game). This would very likely mean that the Ranx Sentinel's factory designation is either "MK I Sentinel" or "MK I Enforcer".
- The Sly Ninja level introduces a flying variant that cannot be hit at all.