This is the 9574th most frequent German word.
mords
"Mords" is a colloquial intensifier in German meaning "extremely" or "tremendously."
Here, 'mords' is used colloquially to emphasize 'Ding' (thing), conveying 'something outstanding or impressive'.
Das ist ein Mordsding, das du da gebaut hast.
That is an amazing thing you have built there.
Here, 'mords' is used to amplify 'Aufwand' (effort), conveying the sense of 'huge' or 'enormous'.
Das war ein Mordsaufwand, alles allein vorzubereiten!
That was an enormous effort to prepare everything alone!
Here, 'mords' intensifies 'Spaß' (fun), implying 'a lot of' or 'a great deal of' fun.