Dead by Daylight

Some simple ways to get this achievement:

The Wraith: Run “The Ghost - Soot” for a lingering six seconds of undetectable after uncloaking. This gives you a generous window to hit a survivor while still affected.

The Shape: Run “Scratched Mirror” and an indoor map offering. “Boyfriend’s Memo” can be helpful to give you a bit more of a lunge, since you barely have one in Evil Within I.

The Ghost Face: Perhaps one of the most intuitive to use. Any hit you land in Night Shroud will count towards this, so run “Walleye’s Matchbook” to reduce your cooldown by six seconds and go crazy.

Some other killers have various undetectable built into their kits, such as The Demogorgon, The Skull Merchant, and of course The Good Guy, but the three listed above will land you the achievement very quickly by comparison, and The Wraith comes included with the game, is easy to play, and requires only one common addon.

Search your perks for ones containing the word “undetectable” as well. Some of these might help even more if you’re struggling.

The Shape (aka Michael Myers) is absolutely the best killer for this, in particular using his tried and true classic "Jumpscare Myers" build.
Essentially what it is is you use the addons Scratched Mirror (Purple rarity, See aura of survivors within 32m when holding the stalk button, but you can't level Evil Within beyond tier 1) and Boyfriend's Memo (Brown rarity, slightly increases tier 1 lung range).
Essentially you'll be permanently stuck in Tier 1, which has its pros and cons.
For the sake of this achievement, you're permanently Undetectable, so every single basic attack counts towards this achievement.
However you can't gain bloodlust and are incredibly slow.
So my build that worked for me goes as follows, though you may have to change out perks based on availability on your end:

Batteries Included (Chucky's new perk, boosts your movement speed by 5% when within 12m of a completed gen).

Rapid Brutality (Xenomorph perk: You gain 5% movement speed when landing a basic attack but can't gain bloodlust ((which you can't get as Tier 1 Myers anyways)).

Save the Best for Last (Myer's own perk: 40% faster weapon wipe speed for every stack gained up to 8, which you get for hitting non-obsessions. You lose stacks for hitting the obsession).

Hex: No One Escapes Death (Universal perk: Once the last gen is done, a Hex is lit and all survivors become exposed, but aren't aware of it until you down someone. You also gain 4% movement speed).

All in all, after already having 10 hits from playing Chucky, it took me 2 games to get the remaining 30 I needed.