Gate to Phyrexia – Antiquities uncommon. Gate to Phyrexia, along with Phyrexian Gremlins, first introduced the threat of Phyrexia to the Magic multiverse with the release of Antiquities way back in 1994. Since then, Phyrexia or its influence has cropped up in more blocks than not: Ice Age, Mirage, Tempest, Urza, Masques, Invasion, Mirrodin (indirectly), Time Spiral, and, of course, Scars of Mirrodin.
Illusion & Reality – Apocalypse uncommon. You know why split cards are ideal for "Pick a Side" Week? Because when you cast them, you literally pick a side to cast!
Side to Side – Unhinged uncommon. The way Side to Side works is that you engage in arm wrestling, then an Ape appears. This doesn't make a great deal of sense, so the flavor text tries to put it into some kind of context.
Fact or Fiction – Duel Decks: Jace vs. Chandra uncommon. When Fact or Fiction was originally printed in Invasion, it featured Squee trying to figure out a map while Hanna looks on impatiently. For the Jace vs. Chandra version, Jace Beleren took over, which makes more sense.
Raging River – Unlimited Edition rare. The moral of Raging River is that in the early days of Magic, there was no such thing as "too many words." And unlike, say, Ice Cauldron, it's pretty clear what the card does!
Jawbone Skulkin – Eventide common. According to the flavor text on Jawbone Skulkin, Kithkin medics sometimes use noggle hoof pulp in their concoctions. This is a little surprising, because Noggles are sentient creatures.
Bonehoard – Mirrodin Besieged rare. Bonehoard builds itself a body out of bones it finds lying around. Close examination of the art reveals that some of its bones are made of metal, and some are made of calcium. Bonehoard doesn't discriminate!
Skull Catapult – Masters Edition II uncommon. According to Fling, a creature will do damage equal to its power when it slams into something. We can further refine this information via Skull Catapult, which seems to assert that no matter how big a creature is, its skull will do exactly 2 damage.
To Arms! – Guildpact uncommon. "To arms" is a phrase that appears in names of three different cards: To Arms!, Call to Arms, and Farewell to Arms. But if you're playing the game "What card names are completely quoted in other card names?" don't forget the exclamation point!
Rally the Forces – Mirrodin Besieged common. Although Rally the Forces is a Mirran card, you might see it pop up in Phyrexian draft decks because of its synergy with infect. This just goes to show how both sides of the conflict can work together for the greater good, assuming "greater good" means "making your deck better."
Myr Welder – Mirrodin Besieged rare. From rules manager Matt Tabak: A Myr Welder walks into a bar and imprints Mimic Vat and our friend the Copper Myr. Wait, you've heard this one? Well, then you know that Myr Welder and Mimic Vat both have a pair of linked abilities. The second ability on each only refers to cards exiled by the matching first ability. The Myr Welder won't be able to use the Mimic Vat's activated ability to produce token copies of Copper Myr.
Rot Wolf – Mirrodin Besieged common. Remember that cute Copper Myr from yesterday? Well today it blocked a Rot Wolf, then had Giant Growth cast on it again. It's now a 2/2 (a 4/4 with two -1/-1 counters on it). Cleanup rolls around, and the effect form Giant Growth wears off. You'd expect to draw a card right? Afraid not. Rot Wolf just has a regular triggered ability, not a delayed one. It has to be on the battlefield when the creature it damaged goes to the graveyard to trigger.
Virulent Wound – Mirrodin Besieged common. From rules manager Matt Tabak: Let's say you have a 1/1 creature that is targeted by Virulent Wound. In fact, let's make it an adorable Copper Myr. You cast Giant Growth in a somewhat futile attempt to save it. During cleanup, the +3/+3 from Giant Growth wears off (at the same time damage does), the 0/0 Myr heads to the graveyard. It's still "this turn," so you'll receive a poison counter from Virulent Wound.
Melira's Keepers – Mirrodin Besieged uncommon. From rules manager Matt Tabak: The damage a creature with infect deals to Melira's Keepers won’t result in any -1/-1 counters, but that doesn’t mean the damage is prevented. If that creature has lifelink, its controller will still gain life. If that creature has deathtouch, Melira's Keepers will be destroyed.