Frost Walker's trigger goes on the stack above the spell that targeted it, and will resolve even if the spell that triggered the ability is countered. You won't want to waste counterspells trying to save Frost Walker.
How “sudden death” works for timed single elimination matches.
Many players will never encounter a timed single-elimination match, but if you do, it's good to know how a winner is determined after the 5 additional turns are over!
Outpost Siege (Dragons) and Perilous Vault.
If Outpost Siege (choosing Dragons) leaves the battlefield at the same time as any of your creatures (e.g., from Perilous Vault), the game looks back to see that it should trigger, and you'll get the 1 damage per creature you were hoping for!
Wurmcoil’s tokens are both named “Wurm” for Maelstrom Pulse.
A token has the same name as its creature type unless whatever created it gives it a different name. So Maelstrom Pulse can kill any "Wurm" token no matter what abilities it has or what colors it is or what its P/T might be!
An interesting situation with Kira, Mutavault, and Tec Edge.
Kira grants an ability to your creatures that triggers when the creature becomes targeted. But if Mutavault is targeted before it actually becomes a creature, it will be too late for the ability to do anything to a spell or ability already on the stack.
Deflecting Palm against lifelink creatures
Deflecting Palm doesn't actually redirect damage, as many players commonly say it does. Since it prevents damage then deals damage of its own, lifelink won't matter for the creature whose damage was prevented.
Flamerush Rider copying Mardu Hearpiercer
Flamerush Rider trigger when it attacks, which means any token copy of a creature with a Raid enters-the-battlefield ability will trigger accordingly when the token is created.
Yasova Dragonclaw pays for the trigger only on resolution
Yasova Dragonclaw's ability is a little tricky. You can't make the controller pay mana for it while not giving up control of the targeted creature. If you have a response, you have to do so after a target is chosen, but before any mana is paid.
Collateral Damage sacrificing Monastery Mentor
Collateral Damage requires the sacrifice as you pay the costs, which is before the game considers it "cast" for trigger purposes. So if you sacrifice Monastery Mentor to pay for it, it won't be around long enough to trigger from the casting, and you won't get a token.