Set mechanics

You control Bothersome Noisemaker (2/2): “Whenever you cast a noncreature spell, amass Goblins 1.” Its job is to grow your Army. In hand: Goblin Plate Mail and Pinecone Strike. You have no Army yet.

You cast Goblin Plate Mail, an Equipment, which is a noncreature spell. Noisemaker triggers first: amass Goblins 1. You have no Army, so you create a 0/0 Goblin Army token, then put one +1/+1 counter on it. It's now a 1/1.

Now Plate Mail resolves and enters, and its own trigger says: “amass Goblins 1, then attach this Equipment to the amassed Army.” You already have an Army, so it gets a second counter (2/2). Then Plate Mail attaches to it: +1/+0 and menace, making it a 3/2 with menace.

Next turn you cast Pinecone Strike (3 damage) at their Ravening Warg. It's another noncreature spell, so Noisemaker triggers again: the Army gets a third counter and becomes a 4/3 menace. The Warg takes 3 damage and is exiled.

The board is clear, so the Army attacks for 4. You only ever have one Army, and every amass card stacks more counters on it. If it dies, Plate Mail stays behind, and the next amass starts a new 0/0 Army.

Storied counts three kinds of things you have on the battlefield: artifacts, legendary cards and Sagas. You have Ori, Keeper of Songs (3/3). Ori is itself legendary (read the type line), so the count is 1 of 3.

You cast Dori, Bearer of Friends. Dori is also Legendary, so the count is now 2. When Dori enters she makes a Treasure token, which is an artifact, so the count is now 3.

With 3, you now "have an enduring story". Ori's text, “As long as you have an enduring story, Ori gets +1/+0 and has vigilance”, switches on, so Ori is a 4/3 with vigilance.

Later you spend the Treasure on Dwarven Mauler, and Dori dies in combat. The count drops back to 1, but the enduring story is permanent: Ori stays 4/3 with vigilance for the rest of the game. You only need to reach 3 once.

Nighthowl Pursuer (1/1 menace): “Ferocious — Whenever this creature attacks while you control a creature with power 4 or greater, this creature gets +2/+2 until end of turn.” You also have Desolation Prowler (2/2). Right now nothing you control has 4 power, so ferocious is off.

Before attacking, you use Desolation Prowler: “Pay 2 life: This creature gets +2/+2 until end of turn.” You go to 18 life and Prowler is a 4/4. Now you control a creature with power 4 or more, so ferocious is on.

Pursuer attacks, and ferocious triggers: +2/+2, so it's a 3/3 with menace. Their single Bear can't block it alone, because menace needs two blockers. It hits for 3.

The deck plays cheap Wolves and a few 4-power creatures (Large Bear, Mirkwood Pathmaker, Ordinary Bear). Once one big creature is down, all the small ones get better.

You control Lakeshore Apothecary (1/2 vigilance): “Whenever you draw your second card each turn, put a +1/+1 counter on this creature.” Your turn starts and you draw normally. That's card #1 this turn.

You cast Patient Instructor. When it enters it recruits: “Draw a card, then discard a card. If you discarded a nonland card, create a 1/1 white Human Soldier creature token.” First you draw. That's card #2 this turn, so the Apothecary triggers. Its trigger waits until recruit is done.

Now you discard. You throw away Velvetwing Butterflies, a nonland card, so you also get a 1/1 Human Soldier token. Recruit is done, so the Apothecary's trigger resolves: +1/+1 counter, now 2/3. (If you'd discarded the Plains, no token.)

Your normal draw is card #1, so any extra draw on your own turn is #2 and triggers these cards (Lakeshore Apothecary, Bard the Bowman, Master's Councillors). Cast your draw effects on your turn. On your next turn, Plunder the Trollshaws (draw a card) would grow the Apothecary again.

Gollum, Silent Slinker is one card with two halves: the creature (4 mana, 4/3 menace) and a small spell, Meager Meal (1 mana: a +1/+1 counter on a creature, and a player gains 2 life). You can cast either half from your hand.

Early on you cast the cheap half, Meager Meal: a +1/+1 counter on Desolation Prowler (3/3) and you gain 2 life. Instead of going to the graveyard, the card goes to exile "on an adventure", set aside face up.

Turns later, with 4 mana, you cast Gollum the creature from exile. You got a spell and a 4/3 menace from one card. (If you'd cast the creature straight from your hand, you'd skip the spell.)

A Saga is an enchantment with numbered chapters. You cast Burn, Burn, Tree and Fern (4 mana). It enters with 1 lore counter, which triggers Chapter I: 6 damage to target creature an opponent controls. Their Ordinary Bear (4/5) dies.

Your next turn, right after you draw, the Saga gets a second lore counter, which triggers Chapter II: destroy target artifact an opponent controls. Their Treasure is gone.

The turn after: lore 3 → Chapter III: add , one extra red mana to spend in that main phase.

The turn after that, lore 4 → Chapter IV: another . After its last chapter, the Saga is sacrificed (goes to the graveyard). While it was on the battlefield it also counted toward Storied.

The opponent has an Ordinary Bear (4/5) and a 1/1 Human Soldier token. You have Desolation Prowler (2/2), and you cast Crude Bent Blade (3 mana).

When the Blade enters: “target opponent sacrifices a creature of their choice”. They pick their worst one, the 1/1 Soldier. (Against a lone big creature this kills it.)

Still in your main phase, you pay Equip to attach the Blade to Desolation Prowler: +2/+1, so it's a 4/3. Equipping only works on your own turn, when nothing else is happening.

On their turn the Bear (4/5) attacks, and you block with Prowler (4/3).

Prowler deals 4 damage to the Bear, which survives, and takes 4, so Prowler dies. The Equipment stays on the battlefield, unattached. Pay again to move it to another creature.