Its blade can extend or retract, being in the form of a dagger when resting, and a full-length broadsword form when at full strength and power. The blade itself is near indestructible, shown to be extremely strong, durable, and laser-sharp. It is able to slice through hardened materials such as steel and solid stone with relative ease.
The blade is also highly reflective, and has reflected Mumm-Ra's own reflection back upon him on numerous occasions. It can shoot blasts of energy with varying abilities and degrees of strength, capable of stunning, electrocuting, melting through materials such as titanium and solid rock, blasting through and apart targets/structures with explosive force, and vaporizing various targets. It has also released enough power to overload the energy absorption defense mechanism of the Plundarian War-Bot and repel and overpower the full firepower of Ratar-O's starship, the Ratstar.
Its power stems from the Eye of Thundera, which is embedded in its hilt. The Eye of Thundera is a ruby that contains an all-seeing, all-powerful, galactic/universal energy force that is sentient in nature, and takes the form of a closed cat's eye pupil when dormant, and opens to become a black cat's head when fully awake.
The Eye of Thundera is the source of the ThunderCats power, and possesses a level of sentience/consciousness that has lead to it being described as "alive". As the Eye of Thundera and the Sword of Omens exist as one in a symbiotic relationship, this has lead to the Sword being described as being "alive" also. When in danger, the wielder can summon the other ThunderCats by shooting the symbol of the Eye of Thundera into the sky, by shouting the battle cry, "Thunder, Thunder, Thunder...ThunderCats - HO!". Upon saying this incantation, the Sword also transforms; the cross-bars of the hilt curl upwards, the blade grows from dagger form to fully sized sword form, and the Eye opens from its dormant to awakened and full powered state, releasing the Eye of Thundera symbol into the sky.
Since the Eye is the ThunderCats' source of power, releasing the Eye of Thundera's signal will give the ThunderCats a great surge of power upon eye contact with the signal. The Eye of Thundera's signal, which is an extension of the Eye of Thundera itself, has many other abilities apart from summoning ThunderCats, such as being able to blast through the full thickness of the planet from its core to the surface in a matter of seconds. It has also been shown to be able to heal as well, and possesses regenerative capabilities; spells cast by Mumm-Ra or others are broken, and if the ThunderCats have been put under any form of trance, mind control, or spells, summoning them with the Sword will break the magic holding them. The Eye contains such immense power that, in many episodes, releasing the Eye of Thundera signal against the enemy or opposing force often results in them being swiftly defeated/destroyed.
The sword possesses many other abilities, such as generating force fields, manipulating temperature to create intense heat or flames, freezing targets in ice, and manipulating energy that it emits to be utilized by the wielder, such as creating bridges of energy and even pole vaults. The sword can levitate and fly, and grants the wielder the ability to fly by holding onto the sword as it travels through the air. The sword has also been seen to transport Lion-O from one place to another, as referenced in the episode Return to Thundera, Part 5. The sword generally grants its wielder any command they give, such as when Lion-O tries to overload the energy absorption defense mechanism of the Plundarian Warbot by commanding the sword with, "Sword of Omens, give me power beyond power...HO!" as seen in the episode Return to Thundera.
Perhaps the most phenomenal feat of power the Sword has demonstrated was in the episode 'Return to Thundera - part 5', whereby the Sword, after being thrown into the eruption of energies escaping from the planets core as a result of the planet tearing apart, managed to hold together those energies, control them, and use its own power to restrain them and revert them back to their normal state, thus holding the entire planet together and saving New Thundera.
The sword can be recalled by its wielder, and will return to their hand no matter how far away it is or what is in its way. It can warn its wielder of danger by emitting a loud growl from the Eye of Thundera. The Sword of Omens also allows its wielder to see across great distances, find hidden things, and spot impending danger or allies that are in trouble with its iconic ability "Sight Beyond Sight", by saying the command, "Sword of Omens, give me Sight Beyond Sight!"
The sword has passed down through Thunderian rule from generation to generation, only ever being wielded by the Lord of The ThunderCats. Its current wielder is the current Lord, Lion-O.
The Sword of Omens is widely regarded and acknowledged as one of, if not the, most powerful weapon in existence. The only weapon to ever truly match it in strength and power is Excalibur, managing to pierce its source of power, the Eye of Thundera, thus defeating it and rendering it useless until Merlin fixed it. Mumm-Ra's weapon, the Sword of Plun-Darr was able to crack the Eye of Thundera on one occasion, but it was easily repaired and in turn, the Sword of Omens has defeated and overpowered the Sword of Plun-Darr on numerous occasions. Hachiman's sword, the Thunder-Cutter, was once described as being as powerful as the Sword of Omens itself, yet since the two have never properly faced off against one another, it is difficult to formulate an informed conclusion. However, in the episode "Excalibur", when Mumm-Ra is desperate to find a power strong enough to destroy the sword, the only weapon that the Ancient Spirits of Evil deem powerful enough to truly challenge the Sword of Omens is that of Excalibur.
The sword's power is so great that Mumm-Ra himself is obsessed with possessing it, so that he may control the power of the Eye of Thundera and become more powerful than the Ancient Spirits of Evil could ever make him, to rule Third Earth unchallenged. However, one of the most iconic characteristics of the sword is that it does not respond to an evil command, and only comes to life to combat evil and, as such, is useless to Mumm-Ra or anyone else that tries to use its power for anything but good. Mumm-Ra is therefore jumping from trying to possess it and manipulate it to his will and trying to destroy it throughout the series.
When the Eye is covered with something strong enough, like black tar, the Sword can be completely disabled, as referenced in the episode The Unholy Alliance However, in the episode Sword in a Hole, this is not a problem, as the Eye of Thundera simply disintegrates its bindings upon being summoned by Lion-O. If used to attack a fellow ThunderCat, it initiates the Curse of Balthas, breaking the sword and causing it to lose its power; the only way it can regain its power is to be reforged in star fire. However there does not seem to be any difficulty in reforging the sword if broken by other means. In fact, reforging the Sword has been shown to make it more powerful than ever before, as seen in the episode Return to Thundera, Part 2.
Whilst usually the Sword is only ever wielded by the Lord of the Thundercats, it has on occasion been used by other characters of 'pure spirit'; Willa of the warrior maidens once used 'Sight Beyond Sight' in the episode 'Garden of Delights', and the Sword has also responded to Lynx-O in 'Ravage Island'. In the episode Tight Squeeze, Snarf used the Sword of Omens with no problem, and the sword in some other episodes have let Snarf contact.