In the Oxygen editor add a Section and inside that, a Repeater.
Set up the WP Query by choosing one of default/custom/manual as needed. Set the Count to 1 less than the number of your desired posts per page. In my test site, I have set it to 5 since the last item is going to be a static div so there will be a total of 6 in the grid.
Click on the Div in the Repeater and set it up with what you want to show for each entry. I have added a Link Wrapper that links to post's permalink with featured image and title inside.
Next, select the Section and add a Div so it is adjacent and below the Repeater.
Add your desired elements inside this Div like image/text that make up what you want to show as the last item in the grid. In my test site, I added static image and text elements, selected the Div and clicked the chain icon and set a link to it.