I did some testing, it seems that its better to drop the Weaker Boss into Global help request. Everytime I did that, the Boss got downed withing 2-5 minutes, whereas when I brought out the stronger Phase 2 Boss, it sometime took even 10 minutes.

I am pretty sure I wont be able to get rid of all the boss summoning currency on time before the event end. To bad I cant just directly exchange it for the one used to buy the items in 1>2 ratio.

Ah well, I`ll try to get all the Manyus, and whatever I can get my hands in addition will be an extra.