Rule rule2 = new Rule(); // initiate the class
    Debug.Log(rule2); //1st debug
    rule2.RuleSetup(r: "CaughtEnough", li: 0); //setting up the parameters
    Debug.Log(rule2.rule); //2nd debug

null
    UnityEngine.Debug:Log(Object)

CaughtEnough
   UnityEngine.Debug:Log(Object)

Invoke(rule, 0f);

CaughtEnough();

public class Rule : MonoBehaviour {

public string rule;

public int leftInt;
public Dictionary<string, int> leftDict;
public float countdown;

public int outcome;

public CatchManager catchMan;
public Net net;

// Use this for initialization
void Start () {
    RuleSetup();
}

public void RuleSetup(string r = "NoRule", int li = 0, Dictionary<string, int> ld = null,  float cd = float.PositiveInfinity) {
    rule = r;
    leftInt = li;
    leftDict = ld;
    countdown = cd;
}
.....

public class Rule : MonoBehaviour{}
Rule rule2 = new Rule();

public class Rule : MonoBehaviour
{
    public Rule(int i)
    {

    }
}

Rule rule2 = null;
void Start()
{
  rule2 = gameObject.AddComponent<Rule>();
}

public Rule rulePrefab;
Rule rule2;
void Start()
{
    rule2 = Instantiate(rulePrefab) as Rule;
}

Rule rule2;
void Start()
{
    rule2 = GameObject.Find("NameObjectScriptIsAttachedTo").GetComponent<Rule>();
}

public class Rule
{
    public Rule(int i)
    {

    }
}

Rule rule2 = null;

void Start()
{
    rule2 = new Rule(3);
}