Voce quer assim teste ai fiz no celular.

local combat = createCombatObject()
setCombatParam(combat, COMBAT_PARAM_TARGETCASTERORTOPMOST, true)
setCombatParam(combat, COMBAT_PARAM_EFFECT, 31)
setCombatParam(combat, COMBAT_PARAM_DISTANCEEFFECT, 12)
local condition = createConditionObject(CONDITION_PARALYZE)
setConditionParam(condition, CONDITION_PARAM_TICKS, 15000)
setCombatCondition(combat, condition)
function onCastSpell(cid, var)
local speed = 200
doChangeSpeed(cid, -speed)
    return doCombat(cid, combat, var)
end

 

não alterou o speed =s