How do I make a cards level realistic?

[Demon From The Void]

How should I decide a cards level?

[Ghost Ryder]

With skills in card-making. You, yourself, can make cards balanced. It can also depend on the effect, and the ATK and DEF stats of the card.

[Guest Ixigo]

Um, I'm going to be VERY general here. This completely disregards effects, so make sure you tie them in if you make effect monsters. But it's a simple formula

 

ATK / DEF: 0-500: Level 1

ATK / DEF: 500-750: Level 2

ATK / DEF: 750-1200: Level 3

ATK: 1200-2000 / DEF: 1200-2100: Level 4

ATK: 2000-2200 / DEF: 2100-2500: Level 5

ATK: 2300-2500 / DEF: 2500-3000: Level 6

ATK: 2500-2700 / DEF: 3000+: Level 7

ATK: 2700-3000 / DEF: 3000+: Level 8

ATK: 3000+: Level 9, but need Special Summoning conditions as well with few exceptions.

 

For levels 1-3, stats don't really matter. For levels 4 and above, you have to choose a "prime" stat for your monster. For level 4 monsters (no tributes), 2000 ATK is generally the limit. For level 5-6, 2500 ATK is more or less the limit, and for levels 7-8, 3000. Defense caps are different as I've illustrated above, but since you'll rarely see a non-effect defender with >3000 DEF, they don't come into play much after level 6.

 

Again, if your monster has an effect, you have to take that into account as well.