All cards revert in magic, not so in Hex. I also don't think you can lose on poison counters in Hex. If you can I haven't come across that rule.
Poison counter workings are a keyword, not a mechanic\rule.
Revert-Upon-Bouncing is all, then. Which, being honest, is a really derivative consequence of being digital and not paper, and not much else.
One key difference in the resource system with Hex vs Magic is if you have 2 Green gems/shards and 4 red, and you have 6 cards that need one green gem in your hand, you can play all 6. In MtG, you can only play 2 of the cards. That's at least once instance of a game system a MtG player would get wrong going over to Hex without reading any rules, but I think the point is a good one, someone who knows how to play MtG, automatically knows how to play Hex, more or less.
I do agree Hearthstone and MtG have about nothing in common, just the fact Hearthstone is played in solitude without interruption from your opponent and has no set attack phase is enough to set it apart from MtG, but the differences number far more.
Differences between HS and MtG\Hex:
- No istants
- No mana colors
- 10 'colors'\classes, of which you can get only one
- No dedicated mana cards
- No noncreature permanents (Artifacts \ Enchantments_Constants)
- Damage doesn't revert after combat
- No upkeep \ dedicated phase structure
- No passing of priority
- Traps exist at custom triggers
[I did not list champion skills, for that they're a difference between HS\Hex and MtG, but not a difference between HS and Hex]
And if we want to go outside the game itself into the supporting structure:
- Draft structure is very different
- Pack structure is very different
I mean, yes. Hearthstone is pretty derivative. But it's not a complete carbon copy with two very subtle changes (Threshold instead of colored mana, and no-revert-on-bounce) and one addition (champion skills)
In addition, no-revert-on-bounce has been proposed in MtG a billion times to fix the underlying problem of auras dying on bounce, but it's unapplicable for a paper game for obvious reasons.
Now, i am not a lawyer, and do not pretend to understand the subtle workings of the legal system enough for that.
But i do question the design ability of someone ripping a whole game wholesale, even if it's a good game in an environment that craves for a well-done version of that game.
A card game lives and thrives on, well, cards. More cards, to be exact. MtG releases cards every 3 months, and for me, the biggest fun in TCGs is discovery - finding new things, making them work (or backfiring horribly).
For that to be done, and for the actual gameplay to be fun with said cards, design and development need to be very competent. Breaking things left and right (Urza's, Mirrodin) is very fun for the deckbuilders, even if it kind of sucks to play. New sets (Innistrad, Theros) are much funnier to actually play, but deckbuilding is.. meh.
If someone rips a game whole, i cannot trust their ability to provide actually good designs for whole sets when the time comes (And it will, if they go forward. We know it will)
That said, i have already fallen in the honeytrap and had given 40$ to the HEX kickstarter, because fuck MODO interface really. But still, i did not expect at the time even the card design to be THAT similar.
e: For the crowd that, like me, wanted something fresh and not a clone: try SolForge (Which, hilariously, is designed by Richard Garfield, which we all know who he is, and developed by Brian Kibler, who won a MtG Pro Tour in 2012, among others.)