Gotta Catch 'Em All!

Question

As I got ready for work today, I had my television on Netflix as I always do. See, the thing about Netflix, they auto-play trailers for the item that is currently in focus. Well, after starting my television (which defaults to Netflix) and heading to the kitchen to make a cup of coffee, I heard the theme song of my childhood. I decided to write a riddle centered around this; however, since I'm also dealing with encryption at work this week, and there's an entire focus on steganography here, I decided to step it up a bit. For today's riddle I'm going to take things up a notch and make an incredibly nested riddle. This riddle (if I'm correct on terminology) will enter the following categories on your journey:

• Rhymes
• Mathematics
• Steganography
• Lateral Thinking

Now, before we get into this puzzle, I'd like to point out a fact to help you along the way.

• This riddle is restricted to the original series.

In order for an answer to be accepted, you must answer the following questions:

• What is the series this riddle is based on (and how did you get this answer)?
• What are all of the names used to find the final answer?
• What two encryption methods were used?

I would like all of these questions answered, as with enough research (and to get the correct answer), you'll be able to answer all three.

Let's begin!

Mom? Mom? Mom?!

Huh, that's weird; my mom isn't home. She left me a note.

Hey honey, I went to the store to grab some groceries; I've written the directions to your destination at the bottom of this note. Oh, and your lunch is on the top shelf in the fridge. Have a great day!

XkW0VMQQalPBPjSUqGVjILWLbeCV3rULXWcMUVD79h/XG6/oCRBzZLBvVI7NIkI5QQ+S9aO3q7+8y7Ei9U/pDzsblOU4e+RTpVywdA/S5zT+q6bSEEA62h94IK776EjInkrdvgKvhYBHfJOjGha0AA==

When we begin, he offers three; the answer to which, number four is the key.

In order to solve it, you'll need more than that; as the answer is hidden with four plus a rat.

It looks like the code is all scrambled up again; I wonder if I still have my old decryption algorithms. Hopefully it's contained to CBC mode.

Oh no! I'm running behind! I need to go get my gAs354j+9c/TFDEke8f53Q==!

To find me just use, your imagination; the answer you seek is from your destination.

You need a new key, currently unknown; my number times four, minus four fully grown.

Hopefully this wasn't too terrible, though I expect it to take a little time. As a bonus question; how did I do on this riddle? Any recommendations for future ones?

Note: Partial answers are okay if you're trying to solve one step at a time. However, only a complete answer will be accepted.

Hint:

I'll use my trusty frying pan, as a drying pan!

Hint:

Consulting with Dexter can be a sure thing; so long as you listen, and don't overthink.

Hint:

A destination you seek, and well it does hide; when it comes to the math, watch it slither and slide.

Update: For the users who don't have ready access to encryption/decryption tools on their computers; there are free online resources available. One of which is Code Beautify.

Answer 1

The final answer is

Arcanine

Here is my reasoning:

Series (From @OfFPiR)

Original Pokemon series

"Four is the key" riddle (From hints and @OfFPiR)

As @OfFPiR says, the offered three refers to the starter pokemon. Of these Charmander is number four in the pokedex (referenced as Dexter in hint 2). This makes Charmander the key. Then "the answer is hidden with four plus a rat", this rat pokemon refers to Rattata which is pokedex number 19. $4+19 = 23$ and looking at pokedex number 23 we find Ekans which is a snake pokemon.

First encrypted message

The ciphertext is given as the longer base 64 string, so all we need is the key and a decryption method. From the previous riddle we know that the key is a Charmander and the decryption method relates to Ekans. Another name for a snake is a serpent which also happens to be a cipher. The puzzle also says that it is in CBC mode. Plugging all these in we find this:

Look for the ghost, unlike no other; it's fearsome, it's mean, and walks like your mother.

Encrypted riddle

The answer is Gengar since he is the only ghost pokemon with legs that can walk.

Second encrypted message

The ciphertext is now the short base64 string. I the decryption method is GOST since it is similar to ghost mentioned in the encrypted riddle. Finally, the pokedex number of the key times 4 minus 6 (Charizad is 6 and is Chramander fully grown) is 94 (Gengar). Solving we get $\frac{94+6}{4} = 25$, which happens to be Pikachu. This also explains why PerpetualJ said I was technically right when I guessed Pikachu in an earlier edit. Decrypting the message gives us Arcanine, our final answer.

Wraping things up here is the answers the questions.

Series: Pokemon
Names: Charmander (key 1), Rattata (clue to decryption method 1), Ekans (decryption method 1), Gengar (decryption method 2), Charizad (clue to key 2), Pikachu (key 2), Arcanine (final answer)
Encryption methods: Serpent and GOST

Answer 2

Partial answer:

Series:

Original Pokemon series.

When we begin, he offers three; the answer to which, number four is the key.

In order to solve it, you'll need more than that; as the answer is hidden in four and a rat.

In the beginning of the series. Ash is offered 3 pokemon to choose from.
But he chooses a fourth one called Pikachu (A sort of rat pokemon).

Now I need to find out how to decrypt this. (I'm not very good with decryption).

Answer 3

Continuing on from @OfFPiR's answer (thanks, @OfFPiR!!) that,

The original series is Pokémon and Ash's choice is Pikachu

I wanted to look at the decryption now.

Having == at the end seems to me like you're using a base 64 cipher, but simply plugging it in to a base-64 decoder does not return a valid result. I think Pikachu has to be a keyword or something; nothing is working so far, but I've used both "Pikachu" and "pikachu" as Vigenère cipher keys on the ciphertext before base-64 decoding it, but it's still invalid.

I'm not really too sure where to proceed after this, but hopefully this helps somebody!