Q: Can I trigger Jarnbjorn after I play an Attack event?

A: Yes. A hero is considered to make an attack both through their basic attack power and actions with the (attack) label. -(Official FAQ)

Q: Will defeating an enemy with Jarnbjorn count as me defeating an enemy?

A: Upgrades are things your hero wears and wields, so when you use an upgrade to defeat a minion that count as your hero (or you) defeating that minion. -(Developer Ruling , Hall of Heroes)

The analysis provided detailing the cost-per-resource aspect of Jarnbjorn is an important thought process, but it does not detail the full value of the card as an upgrade.

One of the most important uses of Jarnbjorn's ability is that it provides an additional source of damage. Minions and Tough often require you to provide damage from more than one lane, and this provides a readily available source.

Further, should you build a physical resource heavy deck, Jarnbjorn will provide you an avenue to spend that extra resource you don't have use for this turn. As victory is decided by damage, it's always useful.

I think it's generally accepted that the average value for non-Hero card damage is around 1.5 damage/cost, with Hero cards reaching closer to the 2 damage/cost range.

Non-Hero Aspect Card Examples

Tac Team

• Cost of 3 (true cost of 4) for 6 damage
• 1.5 dmg / 1 cost

Uppercut

• Cost of 3 (true cost of 4) for 5 damage
• 1.25 dmg / 1 cost

Relentless Assault

• Cost of 2 (true cost of 3) for 5 damage (minions only)
• 1.67 dmg / 1 cost

Melee

• Cost of 3 (true cost of 4) for 6 damage
• 1.5 dmg / 1 cost

Hero Card Examples

Swinging Web Kick

• Cost of 3 (true cost of 4) for 8 damage
• 2 dmg / 1 cost

Supersonic Punch

• Cost of 2 plus 1 to go Aerial (true cost of 4) for 8 damage
• 2 dmg / 1 cost

Photonic Blast

• Cost of 3 minus 1 for card draw (true cost of 3) for 5 damage
• 1.67 dmg / cost

Getting back to Jarnbjorn, at the rate of 1.5 dmg / 1 cost you would need to get 6 uses out of Jarnbjorn to get average value. To get Photonic Blast type value (1.67 dmg / card) you would need to get to 10 uses. Any uses beyond 10 and you are approaching some of the best damage value in the game (but you'll never get to 2 dmg / 1 cost because of the initial 2 cost investment to play Jarnbjorn).

• Cost of 1 (true cost of 2)

• 1 use = 2 damage / total cost of 3

• 2 uses = 4 dmg / 4 cost

• 3 uses = 6 dmg / 5 cost

• 4 uses = 8 dmg / 6 cost

• 5 uses = 10 dmg / 7 cost

• 6 uses = 12 dmg / 8 cost (1.5 dmg / 1 cost)

• 7 uses = 14 dmg / 9 cost

• 8 uses = 16 dmg / 10 cost

• 9 uses = 18 dmg / 11 cost

• 10 uses = 20 dmg / 12 cost (1.67 dmg / 1 cost)

Having to attack first limits it's utility a bit, but on the positive side it does thin your deck out and free up hand space (by being on the board).

Overall, a potentially strong card, but it needs a deck to be built around it. Getting into those double-digit uses will really allow for that positive return on your investment.

Here's what you need to know:

It triggers every time you attack and requires a might resource to deal damage.

QS has Friction Resistance which generates a might resource when exhausted, and readies every time QS does. QS can ready repeatedly every phase.

You can use Jarnbjorn (as long as you dedicate Friction Resistance to paying for it) every time QS attacks to add an extra 2 damage to ANY enemy in play. It far exceeds its cost almost immediately with QS.