How to make the Paralyse rune set the speed to a fixed value?

[badwolf]

local combat = Combat()
combat:setParameter(COMBAT_PARAM_EFFECT, CONST_ME_MAGIC_RED)
combat:setParameter(COMBAT_PARAM_TYPE, COMBAT_UNDEFINEDDAMAGE)
local condition = Condition(CONDITION_PARALYZE)
condition:setParameter(CONDITION_PARAM_TICKS, 6000)
condition:setFormula(-1, 50, -1, 50)
combat:addCondition(condition)
local rune = Spell("rune")
function rune.onCastSpell(creature, var)
    if not combat:execute(creature, var) then
        return false
    end
    creature:getPosition():sendMagicEffect(CONST_ME_MAGIC_GREEN)
    return true
end