The worst Ive ever had was a single card that was listed as Near Mint and arrived looking more in the neighborhood of Lightly Played. You take that as a risk, but you get a huge variety of sellers and the prices that come with that level of competition
Simic Ascendancy can even turn +1/+1 counters into a win condition
Its the Nekusar, the Mindrazer for the Timmy player, the Army typal commander for the Johnny Combos, and fast enough for Spike
But the fact that you have to expend a card to do it is a definite downside
To keep the same Dungeons & Dragons theme deck running, Hama Pashar, Ruin Seeker or Linvala, Shield of Sea Gate could each be swapped from the 99 into the command zone for a completely legal deck
Another expensive but very valuable card is Robin Hood - Timely Contestant as he has a summoning cost of 9 Ink