valuation slip in suits

Do you mean that you have filed a suit
seeking declaration that a particular deed is void or unenforceable.
The valuation slip is not necessary in injunction suits but the same is
mandatory in suits claiming rights such as declaratory suits and suits
between land lord and tenant. In your case as you suit is declaratory
in nature you have to add valuation slips. Mean valuation in the suit
is not sufficient.

it depends upon the rules laid down by each state, normally for summary suits or suits before small causes court valuation slip is not mandatory

Valuation slip is neccessary in civil suits, why because it is the value of the suit you valued it. It is the neccessary slip to be annexed to the plaint. You have challenged the settlement deed to be a fake document, but ultimately you are going to claim interest, possession or title. So there is no hard and fast rule to annex the slip. But to the convinient of the courts it is attached and made it as mandatory one.