I'ma keep going then. Party bus has no breaks. Shredwick missed a card from Theros, so I have to go back at least that far.
I almost feel like I can skip the Battle for Zendikar Block. We got, like,
Zendikar Resurgent,
Zulaport Cutthroat, and...
Void Winnower? I guess? The Tango lands (
Cinder Glade) are good though. They are staples, while the rest of this block is not.
Magic Origins brought some interesting cards.
Jace, Vryn's Prodigy is probably the highlight, but also
Caustic Caterpillar is a staple in green decks (it's instant-speed, and a turn sooner than
Reclamation Sage). There is also
Managorger Hydra for +1/+1 counter decks,
Elemental Bond for creature decks,
Chandra's Ignition for voltron decks, and
Sword of the Animist for... people that don't know better ramp exists.
Moving on, the Tarkir block brought in some tri-color lands (
Mystic Monastery) that many people consider to be staples. Not me. Don't ever associate me with those lands. But this block also gave removal spells like
Utter End,
Reality Shift, and
Merciless Executioner. There were also some amazing draw spells like
Treasure Cruise,
Shamanic Revelation,
Dark Deal, and
Dig Through Time (these are staples). Green decks also got a combo card (
Temur Sabertooth) and a ramp card (
Shaman of Forgotten Ways).
So from this point on, things might get fuzzy, because these cards were released before I started playing Magic.
Commander 2014 produced a true staple,
Commander's Sphere.
Song of the Dryads could also be a staple, but it's price is a limitation for most. There are also people that like
Myriad Landscape. Again, not me.
Core 2015 gave some staples for specific decks, like
The Chain Veil (planeswalker decks),
Waste Not (discard/wheel decks), and
Chasm Skulker (+1/+1 counters/card draw). There was also
Genesis Hydra and
Reclamation Sage for green decks.
Generator Servant works well in any red deck where your commander benefits from haste. Lastly,
Hushwing Gryff is sometimes used as a stax piece.
Conspiracy didn't give anything in the way of "staples", but
Selvala, Explorer Returned,
Dack Fayden,
Deathreap Ritual, and
Treasonous Ogre all deserve a special mention.
Council's Judgment would see play in most white decks, if it didn't have such a high price tag.
And we arrive at the Theros block! You've already brought up
Hero's Downfall, which is a very good removal spell. This block also gave the temples (
Temple of Malady) which work well in some decks (not a lot, and they should not be considered staples). We also saw some staple lands in the form of Nykthos, Shine to Nyx and
Mana Confluence.
Mana Confluence fits well in any deck with more than 1 color.
Sylvan Caryatid,
Karametra's Acolyte, and
Kiora's Follower are staple ramp cards. Some people include
Burnished Hart and
Astral Cornucopia on that list.
Swan Song is a
counterspell that works wonders in commander. Definitely a staple. There is also
Read the Bones for a staple draw spell, and
Gray Merchant of Asphodel as a finisher. Other cards worth mentioning are
Dictate of Erebos,
Courser of Kruphix, and
Archetype of Endurance.
Wrapping this up, Commander 2013 gave the staple boardwipe
Toxic Deluge. This is arguably the best boardwipe in commander. There was also
Darksteel Mutation as a staple removal spell.