BEATING LOKI: Use the Odin ship with the Excalibur weapon and dodge/shoot doing circles around the arena (from time to time you'll have to start doing circles the other way when you see Loki "blocks" your path with his shots) until "device overdrive" special is charged. Then abuse Odin's invulnerability to get to 200k chain so you score 50% + bonus to special when invul wears off. Survive until you can fire special a second time. That last special should get you past him. To unlock Odin, beat Lv 20. To unlock Excalibur, beat Lv 19 with only the first weapon (not as hard as it sounds with upgrades - if you need easy gold, play Lv 18 over and over). IF THIS HELPED COPY-PASTE AND KEEP IT ALIVE :)