Upgrade Seeres as much as you possibly can > Get All in from Nidhogg > Load a map

In no particular order but always prioritizing skills over passives :

Get the skills Magic Missiles + Briar Thorns and their evolutions from Seeres

Get Sentinel + Ball Lightning and their evolutions from Thor

Get Local Ragnarok and its evolution from Odin

Now this is the important part :

The moment you get level 8 hard reroll into finding Nidhogg and getting All in to start staking damage ASAP, eventually you'll have so much damage it doesn't matter and Seeres passive helps cause she doesn't take damage from hits

Bosses get melted in seconds provided you don't get one shotted without shields

Obviously unlocking as many passive skills as possible will help a lot, but this is basically it

Hope it helps the achievement grinders out there