As an OI player that I just came across this thread let me give my two cents on my thoughts about this collab event.

It's unfair for Pero players the same way (and maybe more) it was for us in last event. Personally I couldn't get a single Eromon from the Pero event. This one however raised the bar in difficulty and unfairness even to regular OI players. Normally an event in OI lasts 15 days. This time for an unexplained reason it fell to only 12 days. With one 50% booster (like I have in this one), those 15 days were more than enough to reach about 600-650k EPs. Also there were 3 Areas and each Area that was released gave significantly more EPs than the previous one.

But with 12 days and one 50% booster I'll probably reach 500k in the last day of the event, not even close to 600k that many of you are aiming. Also this event only has 2 areas (the second one will be released tomorrow), which will give more EPs than the first one, but I don't know if it'll be enough to reach 600k for you guys, I just hope it'll be enough to help me reach 500k a little bit earlier to try the harder stages before the event is over.

As a conclusion if you have no booster, you have no chance in reaching 600k unless you pay it big. You'd reach about 250-300k EPs normally by the end of event, so you'd have to cover the remaining EPs by refilling potions (and each one costs 1 euro/dollar). If you have 1 booster of 50% you'll probably need only a few stamina refill potions (about 6-7) but with 2 boosters or one of 100% or greater you have this one easily in the bag.