Yesterday the internet was just glitching. Day 1, wiped out leprechauns with one imp, gathered resources with an imp, took ...

And how did you wipe out leprechauns with an imp? Did you make a mistake? Maybe with Sandrick?
And why didn't you read our discussion here? Everything is written. For example, on the first day, I gained 100 mana for my Hero from the leprechauns. And Zveroboy pulled off buying a second Order Hero and managed to join 5 Fairies to himself.

Day 3, attacked skeletons, wiped out the first group, I had 20 left out of 60 skeletons, bought some more and now have 35 skeletons, but I can't kill the next group no matter what and the hero has no mana. How do you slaughter the skeletons?

Try reading all the posts in this thread starting from the first page — there are only three of them, and look at the rules carefully too. Everything will become clear — there are no secrets here. Zveroboy slaughtered the skeletons with 1-3 fairies, and I did it with one Cerberus.
It's not a pleasant activity — but it's doable :)