The secret to programming is really cut-and-paste. If you have never used cut and paste, you aren’t really using a computer. OK, let’s say I want to program Eternal Witness, what cards have I programmed that are really similar? Well, Gravedigger is 99% the same, so I just copy the code and make a few, small tweaks. Voila, another card is added!! Oblivion Ring and Oubliette are both “brothers from a different color” and I practically used the same code for both cards.
Shock, Char, Psionic Blast, Cackling Flames, Volcanic Hammer, and Firebolt are all essentially the same card, burn is burn. Infest and Pyroclasm both use exactly the same code. Wrath of God and Damnation are perfect twins also. At first glance it doesn’t seem that Terramorphic Expanse and Sakura-Tribe Elder have much in common but these unlikely relatives share the same code. I was curious about cards like Coercion so I also added similar cards like Distress, and Thoughtseize (probably Lorwyn’s most popular chase rare). Mishra's Factory and Blinkmoth Nexus are both lands that turn into creatures, so I copied the code and just changed the specifics like power, toughness, and creature types.
The hardest cards are ones that do something new and weird. Recently I programmed Cranial Extraction, and that code was a little long. It is a really cool card, but it did something brand new, and “brand new” equals “more work.” Each of the planeswalkers are 200 lines because they each had 3 abilities, which is pretty unusual. Incendiary Command was also another tough card, because two of the options let the user choose a target. If Incendiary Command didn’t require any targets, the card would have been a lot easier to program.