Remember, even if you can use Kidou you still need the intelligence to cast it.

Also, shinigami are considered to be proficient with their zanpakutou, no matter the form it takes. So if you change its shape to a spiked chain, you're still proficient with it.

More zanpakutou abilities:

Poison Type: Poison-type zanpakutou excrete and make use of poisons based around the shinigami’s own body and constitution. They use the poisons to cripple or even kill their targets.

Excrete Poison: As a move-action, the zanpakutou excretes a poison that coats the blade. The poison is injury-based, and is expended after the first hit. The poison does one point of ability damage as initial damage and 1d2 points of ability damage as secondary damage. The type of ability damage is specified at the time this zanpakutou ability is taken. The wielder of the zanpakutou cannot be poisoned accidentally, the poison is derived from their body and they are completely immune to its effect. The Fortitude Save DC for the poison is 10+1/2 wielder’s HD+Constitution modfier. This ability may be taken multiple times, each time it gives the zanpakutou the ability to excrete a different poison that damages a different ability score. You may not excrete the same poison again until the poison has been completely used up, whether or not the poison was successful.

Increased Potency: This requires the Excrete Poison ability to take.It increases the potency of the poison excreted by the zanpakutou. It can either increase the Fortitude Save DC by 2, or it can increase the damage type of both initial and secondary damage by one step (1 to 1d2, 1d2 to 1d3, 1d3 to 1d4, 1d4 to 1d6, and so on). This only applies to one type of poison, if the Excrete Poison ability has been taken more than once you must choose which poison it applies to.

Swift Coat: This requires the Excrete Poison ability to take. It allows you to excrete a coat of poison on your zanpakutou faster. You may coat your zanpakutou with poison as a swift action. This applies to any poisons you can use.

Lingering Poison: This requires the Excrete Poison ability to take. The coats of poison your zanpakutou excretes last longer than normal. The poison coat lasts for an additional successful attack. This ability may be taken multiple times; each time it is taken it increases the amount of successful attacks the poison coat lasts for by one. This ability only applies to one type of poison, if the Excrete Poison ability has been taken more than once you must choose which poison it applies to.

Change Poison Derivation: This requires the Excrete Poison ability to take. It changes the ability score the DC of your poison is set to. This functions for all poisons you can excrete.

Change Poison Function: This requires the Excrete Poison ability to take. It allows you to change the type of saving throw required by a poison to either Reflex or Will (Reflex-based poisons use excessive coats of potent poison where trying to turn aside as much of the blade as possible is far more effective than trying to resist it, and Will-based poisons attack the mind itself, and thus can be thrown off through sheer force of will). This ability only applies to one type of poison, if the Excrete Poison ability has been taken more than once you must choose which poison it applies to.

Versatile Poison: This requires the Excrete Poison ability to take. It allows you to excrete poison that is contracted by another method, either ingestion or contact. Each time you take this ability, you may choose another method of contraction. Each time you materialize your poison, you may select the contraction method it will use, and it applies to all of your poisons. Also, you may remove the poison from your blade and apply it to another object, if so desired.

Inhaled Poison: This requires the Excrete Poison and Versatile Poison ability. It allows the poison you materialize to instead linger in the air for one round, affecting anyone adjacent to you.

Poison Cloud: This requires Excrete Poison, Versatile Poison and Inhaled Poison. It allows you to either extend the cloud of poison by 5 feet when using the Inhaled Poison ability or to extend the duration for one round each time it is taken.