Are there any cards that you have played with recently that just seem to perform better than you expected? I don't mean things like hidden gems that tend to be niche finds that fill a specific role for a Commander... I'm talking about cards that you slotted in, perhaps even well known ones,
I slotted Commit // Memory into a deck as I wanted a catch-all removal spell akin to Beast Within or Chaos Warp. Usually I prefer those catch-all cards to cost 3, but I figured I'd let Commit // Memory slide since it would also serve as backup card draw and hand replenishment.
What I found was far more favorable however. Since Commit pseudo tucks, it handles indestructible targets, which Beast Within or Generous Gift would not. Since it can also target spells, its counterspell capabilities have been quite clutch in preventing powerful effects. The hand replenishment has been quite useful, and since the deck I put it in has a propensity to excessively draw, the Memory half has saved me from decking out by re-shuffling my graveyard at key moments.
In similar vein Beanstalk Giant // Fertile Footsteps has been a solid addition to several decks. While 3 mana is a bit slow for a Rampant Growth effect, the ability to not be a dead card is valuable in the later game. I worried that the lack of any keywords at all would make him drastically pale in comparison to something like Ulvenwald Hydra, but granting Trample is practically second nature in green, and the Giant ends up being a prime target for Vivien, Champion of the Wilds or a mutate target for Gemrazer. The split aspect of the adventure allows me to increase both the ramp and threat density in a deck, as well as keeping an available 'free play' on the side should I ever need it.
I also have to give a strong approval to Once and Future. Initially I simply considered it as a Regrowth stapled to a Reclaim (with maybe an upgrade to a double Regrowth), but it ended up being so much more. Having twice the effect on a single card is quite large. Instead of simply replacing itself with another card, keeping your hand even, Once and Future actually gives you card advantage, not just quality. Even more important, the regrowth effect is now at instant speed. Whether it's getting back an important piece in response to grave hate, or being able to set up a play at the EOT and saving some mana from your main turn, or even getting back chief responses when needed, Once and Future has been more flexible than I initially anticipated.
Finally Kogla, the Titan Ape has been a nice package of value when played. Aside from just being a large fatty, the removal on entering means that he trades at least card for card, and the ability to break things on attack is fantastic. I've gotten good mileage out of him even without having humans to protect him. Haste obviously makes him that much better as well, should you run Surrak, the Hunt Caller, or splash into red for Rhythm of the Wild.
Another new one in M21 is Fungal Rebirth. I've found it fits in well in my Saproling deck in that its an instant and gives me 2 bodies (under the right conditions). I feel like its a more versatile card than the Eternal Witness I cut to make room for it.
I'll second the Hex parasite it has done massive work in multiple matches for me.
Feast on the Fallen is a card I expected to stink like doodoo, but it's been consistently triggering in big multiplayer games and really doing things it had no business doing in my +1/+1 counters themed deck.
Colourless lands have been somewhat pulling more weight than I’d expect. Mostly off the back of eldrazi displacer and other eldrazi cards.
More often than not, I find myself out of colourless sources more than coloured sources.
It helps fill the yard early, it helps with random instant speed life-gain when the game is nearing an end and you're opponents are considering final combat math, and in my deck specifically it's a great tool to use when an opponent cyclonic rifts everything back, giving me more junk to toss while looking for a key card.