Plains #343 and #342 (7th Edition), illustrated by Rob Alexander, line up to form a mural.

Plains #331 to #334 (Urza's Saga), illustrated by Rob Alexander, line up to form a mural.

Arena Promos Forest, Swamp, Plains, Mountain and Island, illustrated by Rob Alexander, line up to form a mural.

Judge Gift Promos Plains, Island, Swamp, Mountain and Forest, illustrated by Terese Nielsen, line up to form a mural.

Arena Promos Swamp, Plains, Mountain, Forest and Island, illustrated by Tony Roberts, line up to form a mural.

The two versions of Brothers Yamazaki (Champions of Kamigawa), illustrated by Ron Spears, line up to form a mural.

Snow-Covered Plains and the three Plains of Ice Age, illustrated by Christopher Rush, line up to form a mural.

The four Forests of Mirage, illustrated by Tony Roberts, line up to form a mural.

The goblins on Krenko's Command's art are also in the background of Krenko, Mob Boss's art. Both cards are illustrated by Karl Kopinski.

Spiritmonger was created during the 1999 "Create a Creature" event. Players were asked to design the weirdest powerful creature ever. Eleven cards were selected among 12,000 submissions. Spiritmonger finally won and was printed in the Apocalypse set.

Source

Sword of Fire and Ice, Sword of Body and Mind, Sword of Feast and Famine, Sword of War and Peace, and Sword of Light and Shadow form a cycle that was published across five sets, over an eight years period, from 2004 to 2011.

Waste Not was created during the 2013 "You Make the Card" event.

Vanish into Memory was created during the 2005 "You Make the Card" event.

Crucible of Worlds was created during the 2003 "You Make the Card" event.

Forgotten Ancient was designed during the first "You Make the Card" event, in 2002.

Goblin Grenade's art (Fallen Empires), illustrated by Ron Spencer, has the word "Mike" hidden in it.

Triskaidekaphobia (Shadows over Innistrad) has many references to the number 13.
• 13 nails on the barrel
• 13 logs in the fireplace
• 13 large stones on the front of the fireplace
• 13 small stones on the arch of the fireplace
• 13 pieces of plate on the ground
• 13 streaks of blood on the walls
• 13 wooden planks forming the walls of the house
• 13 cooking tools hanging from the ceiling
• 13 beams on the ceiling

Flame Wave's art by Donato Giancola has two hidden details. There's a giant watermarked skull on the wave and a surfer close by.

Veteran Bodyguard's art (Limited Alpha) was inspired by actor Lou Ferigno.

Counterspell's art (Ice Age) was inspired by bodybuilder Lenda Murray.

Nissa, Worldwaker's art (Magic 2015) was inspired by singer Yolandi Visser.

Presence of the Master's art (Legends) is a portrait of Albert Einstein.

The character on Sylvan Safekeeper (Judgment), illustrated by Pete Venters, is Olle Rade, the winner of the 1996-1997 invitational tournament.

The character on Avalanche Riders (Urza's Legacy), illustrated by Edward P. Beard, Jr., is Darwin Kastle, the winner of the 1997-1998 invitational tournament.