Android.widget,textView cannot be cast to android.widget,button

you are trying to cast TextView to Button.

for TextView do this :

TextView tv = (TextView)findviewById(R.id.your textviewid present in xml layout file);

for Button :

Button btn1 = (Button)findviewById(R.id.your buttonid present in xml layout file);

I added the logcat. But i have no idea what is happening

This is the important information in your LogCat file:

Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
  at com.example.intent_buttontests.PlayScreen.onCreate(PlayScreen.java:110)

You read the error correctly, it is a ClassCastException. The lines below Caused by... tell you where the error was thrown, which is in PlayScreen.onCreate() on line 110. As best I can tell line 110 is:

Button btnBattle = (Button) findViewById(R.id.btnBattle);

But this line is fine and the XML for btnBattle looks fine too...

I ran your Activity with your layout myself and didn't get any errors. Have you cleaned your project? Often this will remove these "phantom" errors. (In Eclipse, Project -> Clean...)

---

I do have one suggestion, you have a lot of Buttons that do similar tasks. You can do the same actions with much less code if you use the XML onClick attribute. First create a method (call it launchClick()) in your Activity like so:

public void launchClick(View v) {
    Intent intent;

    switch(v.getId()) {
    case R.id.button1:
        intent = new Intent(PlayScreen.this, Inventory.class);
        break;

    case R.id.button2:
        intent = new Intent(PlayScreen.this, Equipment.class);
        break;

    // etc, etc
    }
    startActivityForResult(intent, 0);
};

And add the attribute android:onClick to every Button that you should have this behavior in play_screen.xml:

<Button
    android:id="@+id/button3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_toLeftOf="@+id/textViewTitle"
    android:onClick="launchClick"
    android:text="Stats" />

Hope that helps!

Project -> Clean can help you.