Clearly I'm grinding wrong considering I'm nowhere near that even though I'm playing all the time, oh well. I'll get there at some point.
Well I guess I can pass on my personal tips.
1. AI is your best friend for all types of damage dealt/enemies defeated types of things. Just let it (or yourself) run through Endless Towers while you're doing other stuff. However thus particular requirement took me a while, though boss missions that you can repeat might work, though I've personally never done it that way. I have my AI set to 30 combos and counters, and it normally ends quite a few matches in a counter parry, at least enough for me to notice it.
(Also, if you chose to use AI, equip it with Dual Batarang. That way it can't waste meter constantly meterburning it.)
2. Epic Gear is probably your main priority here, and if so, try talking to Stanlos who is somewhere in this thread or the First Legendary Gear discovered is for thread. I was accepted into his clan, and there are 2 buffs the clan has active; Rarity and Double Drops. The Rarity Buff increases the drop chance of Gear when you finish a match, and it is amazing. The majority of the 57 Gear I donated to the Epics sacrificed pool are Epics that I got yesterday by playing either in Guild Multiverse or Endless AI. It is a massive help and it will really help to get those Epics. As I said, I joined his clan yesterday and not even a full 24 hours later I have 50 Epics for Batman,
and that doesn't even include the ones I decided to keep, which is about 20, or all the breaks to eat, go out, etc. They won't drop like candy, but it will certainly be a much more noticeable impact. Plus you'll get other Gear which you can sell to get credit to buy Motherboxes. (During my time typing this particular paragraph I got 2 Epic Batman pieces)
The second buff gives you a chance to double your Motherbox rewards. For example, if you do a tower which will give you a Diamond Motherbox and a piece of Gear, you will have a chance to get 2 Diamond Motherboxes instead of 1. Not only that, but the Multiverse complete can give you additional Motherboxes as well. If it normally would give you 3 Platinum Motherboxes, you have chance to get 4 instead. (I've not gotten 5 or 6, but I've only come across those Multiverses like 2 or 3 times so who knows. Also just got another Batman Epic.) Those Motherboxes can drop more Epic Gear and more credits, and you get the point lol.
So like I said, talk to Stanlos, help in the Guild Multiverse, and you're golden. Just make sure you play with the character you need Epics for. The Gold Motherboxes for Guilds will sort itself out if you do enough Guild Multiverse and are active. I personally am at 61/100 so I'm getting there lol.
3. Multiverse Events completed is relatively simple, I'm under the impression you can simply put the AI to work on the easy 5 fight towers, or some of the Multiverse 3 fight towers, as well as bosses. (If you needed help with that particular requirement, 75 Bosses, just clear out one of rhe top right Multiverses that always has a boss as the final battle. You can redo it, and that's the way I got my 75 Boss Battles with Batman. You could also stop at, say 50, because you'll have done the other 25 by the time you reach 250 Epics, and if you haven't, no harm, no foul, they're really easy to do anyways.) That one is moreso time consuming than it is hard, so that'll sort itself out.
I hope this helps you and others in this thread in any way!