What forms are required to file a petition to modify a divorce decree in Washington State?

See https://app.leg.wa.gov/RCW/default.aspx?cite=26.09.170 There might not be a specific form for that, but perhaps you could start with the...

How do I address a threat by the opposing party in a dispute involving an estate?

Using experience and knowledge are expected. Using position might be improper but it seems unlikely. You should speak with your own attorney...

See https://app.leg.wa.gov/RCW/default.aspx?cite=46.55

Is this money back guarantee written in email legally binding?

In addition to suing for breach of contract, you can sue for a violation of the Consumer Protection Act, RCW 19.86...

Can I sue a hypnotist for hypnotizing me even though I have consented to it?

Consent would probably be a complete defense.

See RCW 7.72 https://app.leg.wa.gov/RCW/default.aspx?cite=7.72

A car accident would not be relevant in an eviction proceeding. See https://app.leg.wa.gov/RCW/default.aspx?cite=59.18

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Am I responsible for damages incurred by my vehicle being stolen and hitting other vehicles?

You might get sued if the plaintiffs think they can prove you were negligent in driving the car, entrusting it to somebody else, or allowing it to...

How can I assist with getting first degree assault charges against my spouse reduced?

You can modify the forms online to make your request: http://www.courts.wa.gov/forms/?fa=forms.contribute&formID=86

Parties in court cases have to obey the orders of the court. Get your copies of the court's orders and read them. If you want the court to change...