I'm not the greatest duelist (Hell, I've only been playing for about a month) but in that time I feel I've grown a little better to the point I can express some of my ideas on the game, cards, community and what not. On this particular post I will be talking about cards I don't see often that I think could go well with certain decks and whatnot. If you have seen these cards used in a duel then cool, but this is based of what I've seen (Or more so what I haven't seen).
Card #1: Chaos Necromancer
I had the idea of this card when dueling someone at school. He was using Lightsworn against my Fairies and won but that's not the point. The point is he is using Lightsworn which require milling cards from your deck.
Example:
Since those cards are going to the grave any monster that goes down will increase Chaos Necromancer attack x300 a card. Of course you'll only want this card later in the duel after a lot of monsters are in the grave. Another thing is that you're gonna want more monsters then spells/traps to make Chaos Necromancers attack as high as can be without putting all the focus on the card because you don't want to put all your faith into one card.
Card #2: Instant Fusion
A very good card in my eyes that I have never seen used. If you willing to pay the 1000 life points you can add a level five or lower fusion monster to the field. Now the only down side is that you can't attack and is destroyed by the end phase but that is where XYZ and Synchro come in. Here is my idea.
Play Instant Fusion and then Emergency Teleport:
So now let's say you have Krebons and Musician King on the field. You can now Synchro for something like Lightning Warrior:
And now that you have a light and dark in the grave feel free to summon Black Luster:
On top of this you still have normal summon since so far everything was a special summon.
That is all my ideas as of right now but I'll most likely think up more in the future.