Level 1: 10 card deck, limit 3, Perk
Level 2: 20 card deck, limit 5, Perk, +1 Hit Die
Level 3: 40 card deck, limit 7, Perk, +1 Hit Die
Level 4: 60 card deck, limit 7, Expert Perk
Level 5+: Perk or Expert Perk or +1 Hit Die.
When your deck size expands on level-up, increase its size by adding extra copies of your cards (up to 4 of any particular card).
When you obtain experience or treasure, you may acquire a card related to the deed that won you that reward. When you acquire a new card, you can add it to your deck and displace a card in your deck into your collection, or scribe the new spell directly into your collection. You can change your deck up with cards from your collection in town, but not during adventures - changes made on the road stay made. You can always add more basic lands to your deck, but only if you've visited and gained experience in that environment. You're assumed to have already done that for the basic lands already in your deck.
Your limit determines the maximum number of lands you may have in play, the maximum number of nonland permanents you may have in play, and both your maximum and starting hand size. It starts at 3 for 1st level Gatherers, and when you play a card past your limit, you must sacrifice a card in play to get back down to your limit. Tokens count towards your limit.
At the end of a dungeon turn (approximately 10 minutes), your power fades. Shuffle your hand back into your deck, and put all permanents you control into your graveyard. Your graveyard and exiled cards only get shuffled back in after a long rest - you don't lose when you try to draw from an empty library, but when you get decked, you'll be easy prey until you rest. If you draw on your power when you aren't in immediate danger, you can arbitrarily cast spells from your deck, but these spells will still go to your graveyard.
Flying, Literally just flies.
Battlecry. Gain an extra action each turn for casting a creature spell or commanding a creature.
Prowess. Gain an extra action for casting noncreature spells or activating abilities and +1 to your hand limit.
Metalcraft. Artifacts you control count towards a new artifact limit rather than your nonland permanent limit.
Constellation. Enchantments you control count towards a new enchantment limit rather than your nonland permanent limit.
Swarm. Tokens you control count towards a new token limit rather than your nonland permanent limit.
Healer. Whenever you gain life, you may heal a creature or another character for that much instead.
Signature Spell. Begin each game with a noncreature spell from your deck of converted mana cost level or less in your command zone. You may cast it from your command zone at any time, and return it to your command zone from your graveyard after a short rest. You may change your signature spell upon discovering a new spell or in town.
Companion. Begin each game with a creature from your deck of converted mana cost level or less in your command zone. You may cast it from your command zone at any time, and it returns to your command zone from your graveyard after a short rest. You may change your companion creature upon discovering a new creature or in town.
Outlast. When your power fades, you may choose a noncreature spell or effect to keep active until the next short rest or when you next draw upon your power.
Recover. When your power fades, you may choose up to level cards in your hand, and begin with them in your hand next time you draw upon your power.
Scavenger. On a short rest, you may shuffle level cards of your choice from your graveyard into your library for each time you've taken this perk.
Champion. Step up the size of your hit dice. You cost 1 less generic mana to attach Auras or Equipment to.
Limited. You may play with the deck size of a level below you (above level 4, you may play with a 40-card deck, but must forego all additional Expert perks gained when you do so).
Mastery. You may upgrade an uncommon in your deck to a rare with a similar effect and color, or a rare in your deck to a mythic rare. GM determines similarity.
Lord of [Type]. Choose a creature type when you take this perk. You may command all creatures you control of that type with a single action.
Conspirator. Once per day for each time you've taken this perk, when you draw upon your power, you may do so with a Conspiracy in your command zone.
Graft. Choose a card in your deck. When you've drawn upon your power, you may put a copy of that card into your graveyard, and gain one of its keyword abilities until your power fades.
Cavalier. When you summon a creature, you may mount and ride it as part of the summoning. When you move, you may have your mount move instead, even if you've already commanded it this turn.
Dash. Once per combat, you may count yourself moving as entering the battlefield for purposes of abilities that trigger whenever a creature enters the battlefield. You may count yourself attacking for abilities that trigger whenever a creature attacks.
If you would be returned to your own hand, you're knocked prone and can't take actions besides crawling around until you stand up. If you would be sacrificed or otherwise die, you're reduced to 0 hit points, no save. If you would be exiled, you blink out of existence, and return when the effect specifies or when your power fades.
Permanents in the command zone are represented by being nearby your character; permanents in the command zone cost mana to pull into battle - whether to draw and charge a magic sword, or to sway an ally to fight at your command.
Unlimited Power. You have no limit for controlling noncreature permanents, including lands. Requires any two of Metalcraft, Constellation, Landfall, Swarm.
Spellstorm. You may spend one action to cast any number of noncreature spells (you still pay all costs for the spells). Requires Prowess.
Permanence. The effects of your noncreature spells don't dissipate until a long rest. Requires Outlast.
Commander. You can play a 40-life, 100-card singleton Commander deck; your companion creature can be any legendary creature. Requires Companion and enough cards in your collection to build a commander deck.
Epic. Once each turn, you may cast a copy of your signature spell from the command zone. You still pay all costs for it. Requires Signature Spell.
Eternal. At the end of each short rest, shuffle your graveyard back into your deck. Exiled cards remain in exile until your next long rest. Requires Scavenger.
Regenerator. At the end of your turn, you may have each of your damaged creatures regain HP equal to their toughness. Requires Healer.
Devotion. Add up to four copies of a legendary creature of your choice to your deck. Requires Mastery.
Replicate. Choose a card. You may have any number of that card in your deck.
Deckmaster. Add a copy of a banned card to your deck.
Latent Spark. A planeswalker takes notice of you. Add up to four copies of a planeswalker card to your deck. They eagerly await the awakening of your spark, so you can aid them on their travels through the multiverse. Activating a planeswalker's loyalty ability does not take an action - but calling upon planeswalking friends invites dangers from the rest of the Multiverse...