I think it's balanced as long as it doesn't stack.
If it the upped one in particular stacks, the damage ramp gets really insane.
If you have like 3 Temporias out, you're dealing 6 damage already per attack, which means you're almost guaranteed to outrush your opponent if he doesn't have anything higher than 6 ATK.
On the flipside, it's a 2 card combo. See below comment and calculation for more explanation on why I have the card costed as is.
This card claims that on average over a thousand games with this card, the average extra damage per turn would be around 4|6. I think this claim is a little on the low side however playtesting would identify this and a minor cost increase would fix it if it exists.
(Note that this comment was made prior to lots of changes in the game like the Dragonfly buff.)
Cost = Attack Value + Skill Value + Bonuses
(I'll assume that the average damage is 4 | 6)
Unupped
Attack Value : 4
Skill Value : 4 (+4 damage)
Bonuses:
- Single Slot -3 (aka only works in the Weapon or Shield Slot)
Final Value: 5
Upped
Attack Value : 4
Skill Value : 6 (+6 damage)
Bonuses:
- Single Slot -3 (aka only works in the Weapon or Shield Slot)
- Upgrade bonus -1 or -2.
Final Value: 5-6