The TokTz-xil-ak (also known as the Obsidian splitsword) is an obsidian weapon, and is stronger than the rune sword and equal in power to the dragon longsword. Level 60 Attack is required to wield the Toktz-Xil-Ak. Its accuracy increases by 30% against TzHaar-Xil that use that weapon (meaning that the ranged TzHaar or the TzHaar wielding the TokTz-Xil-Ek are not affected).
It is affected by the Berserker necklace, receiving a 20% damage increase when the necklace is worn.
With the advent of the Evolution of Combat, all Obsidian weaponry was updated to have equal stats to Dragon weaponry, and so the only real difference between a Dragon longsword and a Toktz-xil-ak is the attack type, which is stab as opposed to slash, and the lack of a special attack.
When combined with usage of the Berserker necklace, damage output can be significantly increased, and in some cases may be a better choice than a Dragon longsword or an Abyssal whip, even taking into consideration the accuracy loss from using stab on a slash-weak monster. Once, players might have had to worry about loss in accuracy and defence when trading an Amulet of glory or an Amulet of fury for a Berserker necklace, but since the bonuses of both have been changed with the release of the Evolution of Combat, players now only have to worry about the loss of a 30/32 strength bonus (which the 20% damage bonus of the Berserker necklace far outweighs).