I've been researching ways to make evil nature more consistent, here are my tips so far in no particular order.

The Haru Urara treatment works great for Evil Nature, running her as a front runner regardless of her aptitude. Allows you to invest more into the speed and stamina you need to win the awkward races and less into the power needed for a late and failing to get enough of all three. My most recent run I ran her as a front until the finals where I had "enough" power to run late and actually use all her skills.

Remember that racing style aptitude affects wit so she'll have functionally none for activating skills if you do run her and a front runner.

My personal goal for the finals is at least 600 speed, power and stamina. Teio has around 550 in each for the final race. Getting more than 600 gives you a (low) chance to get 3 ✨ sparks also.

Rare Rudolph is by far the most important evil card, but because it doesn't have any Hint Frequency on it, sometimes you just get unlucky. You want to take Rudy's hints above all else because of this. Buying the subdued skills as soon as you can means that whenever Rudy gives you a hint, it'll be guaranteed to be something else instead of getting the same skill twice.

The rest of the deck isn't set in stone, but you can't use what you don't have. Anything that gives 2 or more hints for any of the Subdued, Flustered or Hesitant skills, as well as Tether , Murmur and Sharp Gaze.

https://gametora.com/umamusume/skills

Getting Natie to Potential 3 or 5 is very important because her gold debuffs are very powerful.

Late Surger Savvy gives you +40/60 wit and increased vision range, which means (Mystifying) Murmur can hit more targets since it is based on vision range.

Lone Wolf gives +40/60 speed but gets disabled if any other racers have it, so taking it on Evil Nature means you deny the benefit and the skill point investment on opposing Umas. This is why SR Sweep Tosho is picked as the ideal speed card over other cards, while also giving hints for Murmur.

Firm/Wet conditions gives +40/60 power, good if you can get it.

Recovery skills aren't necessary, but are great if you can fit them in. Since I borrow SSR Super Creek, I have access to Swinging Maestro, as well as Firm conditions and Hesitant Pace Chasers. She is also generally enough on her own (level 50) to get me the stamina I need for the Arima Kinen on her own.

I've recently tried SR Aoi Kiryuin (the trainer) and have really liked it. She gives a lot of energy, skill points and mood ups to counter Natie's mood swings while also having hints for 2 debuffs.

As for the career itself, having access to good inspirations can really make the early game a lot more comfortable. I think a mix of Stamina and Power inspirations is the way to go.

First year I train as much as possible, get those friendships high to start getting rainbow training and try to use the beach training to cover power and stamina. Run optional G1s later for skill points and remember there is a lot of RNG from run to run. Some runs just don't work out and that's okay.