Fisherman

You've mastered the art of fishing on a mental and spiritual level, allowing you to utilize your fishing rod as though it were an extension of your immortal soul, a line that can be threaded through both space and time, the universe opening before you to welcome you with open arms. Fishing is like stealing but with more precision in method and less precision with intention, and is usually done with a fishing rod or net. It's also usually done to catch fish, but the Dimensional Fisher has learned that a fish is nothing more than a concept, so really anything is a fish if you really think about it. And you know what? Things like location on a physical plane or temporal moment are also concepts, so a Dimensional Fisher ignores those things to. All that matters to them is catching what they need. 

Pocket Fishin'

Starting at 3rd level, you can attempt to make a Slight of Hand check to pickpocket a creature who is currently within 300 ft from where you stand by sending a fishing line and tackle through a dimensional rift leading into the creature's pocket, or next to their waistband. On a successful Sleight of Hand check, contested by a Perception check of the target, the item you retrieve through this method is determined either by you, if you can see the target, or by the DM if you can't. 

The Pond

Starting at 3rd level, you have gained access to the Pond, a small pocket dimension of water teeming with fish. A number of times per short or long rest equal to your proficiency bonus plus Dex or Str, you can fish in the small Pond, and gain a "Fish" of your choice. 

Boom Fish - A small, round fish, with the intrinsic ability to explode outward when afraid. Within a 10 foot area, deal 3d6 cold damage, with a Con save DC of 15. Usable once.

Talking Angler Fish - A tiny fish, with a bit of a mouth on it. Roll 2d6, and choose that many allies or enemies to gain either 5 temporary hit points, or take 5 psychic damage.

Sardine - A tasty, if not smelly. Roll a d10, and gain that many sardine. Each sardine can heal 1d4+1,  and spoils after an hour if not canned. You can eat 3 at a time.

Old Can - Your not sure why this is in here, but it sure is useful. These cans look however you please, and can hold up to 5 fish.

Golden Fish - These fish each can be sold for a measly 10gp, or attached to your wishing rod, enhancing your next 5 attacks with 1d4 radiant damgage. Very cute.

Helmet Crab - You can wear this small bottom dwelling crab, as a hat! You gain 2 AC,  but this item counts as a hat. It stays with you for an hour, then scuttles away to your Pond. 

Lost Rat - A small, very angry Giant Rat. Attacks anyone within 5 ft of it, so get rid of it quickly! (This rat uses the stat block of a giant rat)

Puffer-Fish - Nobody likes this fish. When squeezed, this fish secret's a poison, and can be used 3 times till returning to the Pond. (The poison is Assassins Blood).

Angel Fish - Just as talkative as the Angler Fish. When using this fish, everyone you chose within a 30 ft cube, must make a 15 DC charisma saving throw. On a fail, they are charmed.

Good Ol' Boot - I don't even know. With this "fish", you can put a single fish in, and shake real hard, enhancing your fish. +2 to all DC's. Anything without a DC doesn't change.

The Fishtail

You have spent a lot of time, money, and effort, to teach your fish how to help you be sneaky and such. You gain the Find Familiar spell, but can only summon a small quipper, with the ability to grow legs, that gives the fish a 20 ft walking speed. It also gains a +2 to any stealth check, and a +5 to perception checks. Beyond this, it functions as a normal familiar. 

Fishy Toss

Starting at 13th level, you've come to understand the subjectivity of all fish to a degree that allows you to convert the very concept of damage into fish, allowing for easy storage. If an enemy attempts to attack you but fails, you may use this feature to turn the concept of that concept into a fish and stow it in your Creel, a basket that holds fish. The fish exists for one day. You may attempt to throw a fish in your Creel at an enemy as though it were a simple ranged weapon, and on a hit, it deals your sneak attack damage, then dissipates.

This ability can be used a number of times equal to your proficiency bonus.

Rollin' Down the River

At 17th level, you can summon the big kahuna, the rough and tumble, boss of all bosses. You gain the ability, as a full turn, to give up a number of fish that you choose, and summon the Froghemoth, which just uses the Froghemoth stat block. This mighty warrior stays with you as many turns as you offered fish, then displeasure arises as it realizes you have no more fish, and jumps back into your pond, to sleep. It regains all HP and abilities at the end of your next rest.