I love the card! Assuming that shield effects activate twice is a practical -1 to attack, then we have a 4
for *5 attack and 6
for *10 attack. Finding equivalent cards, one second...
*5/2 vs. Sapphire Charger: 5/4; the first cost 4 while the second cost 5. One quanta is not worth two health, however it is worth two health and momentum. Unupped is fine.
*10/4 vs. unupped Amethyst Dragon: 10/5; the first cost 6 while the second cost 10. One health is not worth four quanta. I don't care how many counters there are to this, one health is not worth four quanta. This is
including the fact that shields activate twice.
I like the card, but you should increase the cost of the upped to 8. The only reason it isn't 9 or 10 is because it's upgraded. 8 should do fine.