Notion Thief confuses many people, and dredge isn't much better... When the two come together, you get this rules tips blog!
You can’t “miss” True-Name Nemesis’s “as this enters…” ability.
True-Name Nemesis doesn't have a triggered ability, so it's not possible to simply "miss" the ability. If you think your opponent failed to choose a player, you must mention it.
Gargoyle Sentinel can dodge Clear a Path.
Clear a Path needs the target to have defender both when you cast it and when it would resolve. Gargoyle Sentinel can make sure the latter part isn't true in order to survive!
Casting Ajani’s Pridemate while you have Staff of the Sun Magus – No counter for you!
The Staves all trigger when a spell is cast, so that trigger must resolve before the spell that caused it to trigger can resolve. If you cast Ajani's Pridemate, you gain the life before it actually enters, so it won't be around to trigger on that life gain and therefore won't gain a counter.
Resolute Archangel vs. Erebos
Setting your life total to a higher number counts as gaining life. So if you're unable to gain life, there's no way for your life total to increase.
Don’t distract players mid-match.
Players are expected to play their own games, so resist the urge to comment on ongoing matches or provide play advice.
Bestow cards are not auras in your library.
When you're searching your library for an aura card, it has to have aura printed in the type line. A bestow card doesn't qualify!
Prerelease Week: Returning mechanics – “as long as you control…”
The new core set brings back the creatures that get a bonus from "friendly color" lands. Be sure you know when the game cares about that ability and when it doesn't!
Prerelease Week: Returning mechanics – Indestructible
Remind yourself about the subtleties of indestructible (including the M14 change), since this keyword ability returns in M15 (alongside Turn to Frog, no less!).