E-104 Epsilon (E-104 "イプシロン" E - 104 "Ipushiron"?), or E104 "ε", is an orange E-100 Series robot. E-104 Epsilon is re-equipped with twin STINGER missile launchers on the arms, which are useful for taking out moving air targets, and a Jet Booster.


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E-104 Epsilon being discarded.

Like E-102 Gamma, E-103 Delta and E-105 Zeta, Epsilon was first a recolored clone of E-101 Beta, but after being discarded, he was re-equipped with upgraded twin STINGER missile launchers, a Jet Booster and a target locator. After Gamma was proved superior, Epsilon was teleported to an unknown location along with Delta and E-105 Zeta. Later, Gamma found Epsilon in a lava-filled cave in Red Mountain on Angel Island. The two fought, and Gamma emerged victorious. A Flicky inside was released after Epsilon was relieved of duty.


Boss guide

Close the gap on Epsilon. He can fire homing missiles more quickly than his predecessors. If you stand too far away, Epsilon continues to fire missiles, which interfere with your ability to target the robot. To quickly end the battle with Epsilon, get near him. When you score a hit, wait just long enough for Epsilon to shake it off, then fire again. If you are not pressed for time, you do not need to stay over him. Just face Epsilon to quickly target any missiles.


Sonic Adventure Boss 14 - E-104 Epsilon

Sonic Adventure Boss 14 - E-104 Epsilon

In other media

Archie Comics

Sonic X


  • Epsilon's Sonic X design is near identical with his game counterpart, with minor alterations to his double cannons.
  • Epsilon is the fifth letter of the Greek alphabet and E-104 Epsilon is the fifth E-100 robot made, the numerical descrepency from the model numbers is due to the fact E-100 Alpha, better known as ZERO, is still considered an E-series unit.
  • Although Epsilon's later weapons are visibly different from Beta and Delta's missile launchers, they function identically.
  • Despite his lock-on ability in his upgraded form, Epsilon visibly lacks a targetting sight like Gamma.
  • Although he no longer has a functional forearm due to his missile upgrade, a mirror reflection of Epsilon's original forearm still appears on his front skirt plate. This is due to the fact the reflection is an actual painted image within Epsilon's texture, which was repurposed from Gamma's textures.
  • Epsilon also seems similar to the robot, Isaac from the Archie comics in terms of color. Though Isaac also looks like Gamma and colored a glossy gold instead of Epsilon's rusty orange color.
  • His Jet Booster seems to let him fly for a short time, instead hovering of like Gamma's.



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