Toxic this and toxic that… So, just what is “toxic” anyways?

It's easy to point your fingers at some examples. Sihil is toxic. Kittyspam is nerfed, but still toxic. But what makes, for example, Aerondight toxic but not Dragon's Dream? Arachas Queen toxic, but not Eredin? Is Viy still toxic? Raffard's Vengeance? Gezras? Whoreson Junior? Highland Warrior? (Spoiler: Highland Warrior is completely toxic.)

What qualities make a card toxic, as opposed to a little too powerful, or played more than average? I think a toxic card has to have several things going on at once. I'm going to start a list, and if you can think of any other factors, add them to the discussion.

1. Toxic cards will usually be cards that are very difficult or impossible to counter. Obviously the reverse isn't true. If I give a card a big boost of Vitality, and you wipe that out with a Pellar, or just destroy the card with Epidemic, nobody is going to say that's toxic. But a card like pre-nerf Whoreson Junior that could just wipe out half the cards on your side on deploy was very Toxic.

2. Toxic cards often will be far too powerful compared to other cards of the same provision value. And "too powerful" should not be taken to mean "has too high of a ceiling". Some cards in some circumstances have ceilings of over 5 digits, but they are not considered toxic. "Too powerful" means that the typical play creates and/or destroys too much power per provision. Highland Warrior only plays as a 3 + 1 armor for 5, but it typically creates six or more points of carryover and since it is Bronze, it can be played twice and is easy to replay at least once.

3. Toxic cards often require no setup and/or no skill to use. Again, not all cards that have this feature are toxic. It doesn't take any setup or skill to drop Alzur's Thunder and damage a unit by 5. And this is not something that is a feature of all toxic cards. Renfri required a lot of attention and consideration in order to express its highest value.

4. Toxic cards are often binary – counter and win, or don't counter and lose. Some cards will not be like No. 1 above, but will still be very toxic. Pre-nerf, if you did not win R1 and bleed out either Tunnel Drill or Cleaver on R2, you were almost certainly going to lose R3. And there have been plenty of cards that needed Heatwaved R1 or they would be replayed on R3.

I was going to add that toxic cards make a season all about one card or deck to the exclusion of others, but that's really a side effect of No. 2 above.

Anything I'm missing? Anyone want to make a case for any of the cards I mentioned not being toxic? Or make a case for cards I didn't mention being toxic?