Hearthpwn

I agree with a lot of what you say.  I especially agree with the idea that there should be an ebb and flow over expansions with regards to tribal synergy. I would contend, however, that the way to do this isn't by restricting keywords to a tribe, but by printing some tribal cards rather than others. Just because you expand possibilities does not mean that all possibilities need to be realized every expansion.

The pool of keyword mechanics in Hearthstone is pretty small by design. To call elemental and dragon synergies "conditional battlecries" collapses the significance of elemental: "played last turn" and dragon: "in hand" . The magnetic keyword is pretty close to "Battlecry: If you control a mech, give it x" [if not, play a worse version, which is exactly what you do if you don't meet the conditional battlecries for elementals and mechs]. Board presence is actually what the mech synergy has always been since GvG, so in that sense, Magnetic is nothing new.

Yeah, I don't mean to trivialize the differences today between tribes by abstracting their effects to battlecries. There are obviously different design philosophies beyond "what condition triggers my battlecry?" - Murlocs tend to be aggressively stated and designed for zoo style decks, for example. 

That said, having restricted keywords is not new. "Combo" and "Choose one" are special keywords for specific classes, and "Adapt" is a special keyword for Un'goro. All of those abstract to some kind of custom battlecry on a minion*, but are ultimately narrowly applied to ensure some "core identity" for the thing being identified (Rogue, Druid, and Un'goro respectively).

*"Combo" and "Choose one" can also appear on spells, but since Mechs are always minions, it's not necessarily useful to think about those cases. Both keywords could be replaced with battlecries on minions and still exist for spells. Also, they could presumably print a spell that magnetizes mechs, similar to how Evolving Spores adapts minions.

Quote from Ryan_Sechrets >>

The idea of a card that is either a minion or a minion enchantment is a great one! It offers flexibility like Discover, prevents dead cards in your hand, and generally encourages more in-game decision-making. Therefore, the idea of the Magnetic keyword has a lot going for it!

The problem is that Magnetic is limited to the mech tribe, arbitrarily restricting the design space for use of this keyword mechanic in future expansions. We saw this problem before, after GvG, the mech tribe received little support. If that happens again, this would be Blizzard introducing a new keyword with limited use, and Blizzard has said that they want to limit the number of keyword mechanics to keep the game accessible (I'm looking at you, Enrage).

Here is a simple proposal to improve the mechanic: Call it "Fuse" and have it always specify a tribe (or tribes). For example, this is how the card text of the new card, Spider Bomb would read: 

Fuse: Mech

Deathrattle: Destroy a random enemy minion.

This would allow for many more interesting card interactions. Sure, some could be problematic. Don't print them!

What are your thoughts on Magnetic? Do you have a better idea to improve it?

To sum up your argument (keep me honest, please), you believe the "magnetic" mechanic is a good mechanic, but that it should be open to all tribes in Hearthstone so it can stay relevant even if Mechs fall out of favor.

From a design philosophy standpoint, I completely disagree. Giving mechs a unique game mechanic is exactly what Blizzard should be doing to make tribal synergies more interesting. Today, most tribal synergies exist in the form of conditional battlecries - yes the conditions are different ("hold a dragon" vs. "played an elemental last turn," etc.), but in principle there's nothing fundamentally different about those tribes. Maybe they should add unique mechanics for other tribes to better differentiate tribes, but making this mechanic generic to support all tribes ruins the "specialness" of it.

Regarding whether or not the broad support of mechs over the last few expansions highlights a problem, I think the opposite is true. It's great to see that mechs will get a lot of support now, and that at some point that support will rotate out of standard to make room for some other tribe and/or mechanic to be front and center. It's okay for the support of certain aspects of the game to ebb and flow to keep things fresh.