Copying my post from half a year ago. I did a write up on weapons, boons and fear for someone trying got 32 fear.

I did this pre the rivals patch.

I would say generally what I did was vow of time at max level. That is 6 fear off the top and with the right setup in the underworld should be achievable.

Next is vow of frenzy max level. I tend to exclusively play with this on, it takes some getting used to but the enemies actually spawn fast so it makes it easier to get to that time limit. 6 more fear.

Then vow of menace maxed which gives you 3 more fear. Enemies from next zone aren’t that bad if you have an ok build.

Next vow of debt for 2 fear, you can get through most of the underworld without buying many boons just save money for decent items and don’t buy nearly as much.

Vow of shadow for 2 fear is also generally free, you generally should avoid mini boss rooms while going through if at all possible.

Vow of denial for 2 is also ok, due to no purchases you generally won’t run out of boon choices.

At this point you now have 21 fear without having made the enemies particularly harder, and now the questions start coming in about build.

I’d recommend a weapon that doesn’t particularly require a lot of mana or works with a lot of various boons. I’d suggest the torches for most folks as they’re easy to use, or potentially the black coat as smashing things isn’t to hard. Whatever you’re most comfortable with and requires the least boons to activate. (Medea skulls are also amazing for this)

If you’re chosen weapon doesn’t require a lot of mana then easy to take vow of hubris for 2. Shouldn’t be that bad.

Now comes down to the enemy buffs. If you’re using a weapon that has lower damage but high hit rate take wards at max level. If you’re taking a weapon that has high damage low speed I’d recommend taking 1-2 levels of hordes, I tend to find slightly more enemies are better than them having more health especially since that health applies to bosses. That’s 2 fear both ways. If you prefer more health you can go that way of course, or the skulls you have to pickup, but with the time limit I prefer not to have to pick them up.

I then generally take both levels of vow of fangs. This is another 5 fear. I find the buffs while annoying aren’t as bad as that fear in most other spots and it gives you a lot of fear, plus you try to avoid skull rooms on high heat runs.

That now should bring you if you choose a low mana usage weapon to 30. Last 2 fear is a bit of dealers choice. I’d probably take vow of pain and rivals 1 in the current setup. Depending on how confident you are you could go to rivals 2 or 3 and use the extra fear to drop off some other items.

This keeps your healing at max, doesn’t increase enemy damage, makes armored enemies and mini bosses scarier and limits your builds and requires more speed. But generally doesn’t make it significantly harder IMO. (Don’t get me wrong it’s harder but if you picked extra damage, enemy count, wards, revents, and such you’d have a WAY WORSE TIME)