What would be a good pokemon to introduce to someone who is afraid of them? Not a Garchomp, I’d assume?

Definitely a garchomp. The best way to overcome fear is by exposure, yes?

Edit: According to my editor, I should be ashamed of myself, so allow me to give you an alternative answer.

There are two possible routes you can take. The first is by giving them a starter, preferably from your regional professor. Many starters handled by Professor Oak and his colleagues have been bred for the express purpose of being partnered with extremely new and young trainers. Many new trainers only know the very basics of pokémon care, so each starter needs to be not only resilient but also tranquil around humans, even those who are particularly excitable. So if your friend (or whoever) is panicking, a starter would be the least likely to react to that panic.

Some starters, particularly the bulbasaur line, also evolve into forms equipped with certain abilities that have calming effects on nearby humans. Bulbasaur in particular eventually becomes venusaur, which is known for its highly soothing scent. This will also help keep your friend calm as they interact with not only venusaur but also any other pokémon around them.

Alternatively, there are plenty of other pokémon that possess other calming abilities naturally or are otherwise bred to be as calm as a starter. Take the happiny line, for example. Chansey and blissey especially dedicate themselves to calming and comforting others, and many individuals handled by breeders have gone through at the very least extreme basic training in pokémon nursing. That is to say, any chansey and blissey you obtain from a breeder has likely been trained to handle nervous or scared pokémon and humans, and thus, they’re highly empathetic and knowledgable about how to handle a human who might just be terrified of them. Bred audino in Unova receive similar treatment, as do jigglypuff and wigglytuff in Kalos. The togepi line also has a natural inclination to make others happy as well as an in-born sense of empathy, but some specimens may get a little too excited over the prospect of cheering another up.

Meanwhile, your other option is using a species that possesses other natural abilities that can calm a human being. Blissey, for example, lay eggs that can eliminate feelings of sadness and fear with just one bite. Alternatively, it can also use Heal Pulse, which while better known as a move that heals wounds, can also help a subject to relax. Other species that possess calming abilities include chimecho (who can emit sounds capable of calming even rampaging tyranitar), bellossom (who can emit soothing aromas), and gardevoir (highly empathic pokémon with the ability to project calming psychic waves).

The point is, anonymous, get a pokémon that’s been trained (or bred) to deal with nervous humans or a pokémon who can help a human enter a calm state of mind. Either of these kinds of pokémon are perhaps the least threatening ones in existence, so they would make excellent introductions for someone who would like to be exposed to pokémon but also suffers from poképhobia. Ideally, though, you’ll want a pokémon who can be both soothing and capable at dealing with humans, which means that out of all of the above mentioned creatures, chansey or blissey may be your best options.

Good luck, anonymous.