Reached GR level 20 on T4 in the trial and finished it in time...but also choose to upgrade my main gem.
I found the Grin Reaper mask and really think it helps me a lot. I am currently experimenting with my built and already find a nice modification:
when the skeletons are summoned, they also use the attacks I am using - but only a few of them, not all are possible. For instance, they use all the primary attacks it seems. But they also use the zombie bears for instance. But what works quite well: I included now the spider queen attack. I can only summon one of these at a given time, but it seems that my friendly skeletons can summon as much as they want!! So I did runs with 15 fetish and 10 spider queens running around and finishing basically everything in my way.
I have one slot where I am experimenting atm, but can't find anything good so far: I hoped the skeletons also summon the giant...but they don't. I replaced it with the bears...and it seems to work quite well. But I am still searching for an improvement like the spider queen...any ideas?
My toughness is about 11.8 million. My attack is about 640k. But my life per second is only at 340k or so...this is quite low, but it seems that this is not so important for T4.
I also hit paragon level 93...still a long way to go.
Also, grinding for good gear is meh!