Looking at Goof’s tutorials “Use Game Guardian to unlock playmats” and “How to inject 3 cards you don’t own into your deck” you just need to a mixture of both.
>Start a duel with 20 card in deck, and have Block attack as 3 of the cards.
>play the card block attack on any monster and one the play animation is done.
>open GG and select memory range at the very bottom to just ANONYMOUS.
>select search tab in GG and New Search for the following (4874;0;0;0;0;0::21), Type: Dword(-2,147.483.648 – 4,294,967,295) and hit new search
>should get a few results with the first being a 4 digit value and rest being 0
>click on the 4 digit value and change it to the value of any Light Monster (3800 is Blue Eyes White Dragon) and click yes
>once the value is changed click and hold on the same value, select Offset Calculator
>in the calculator type in -40 (minus 40) and click goto
>select the first result and change it to 200.
that should be all you need.
PM if you’re having trouble.