Hearthpwn

Card generation from other classes:

Swashburglar - 1 drop and a free card for your Tess.
Fool's Gold - Nerfed with the new card pool introduced in Perils of Paradise, but still a decent way of generating two minions for cheap. The 3 mana armor pirate is an amazing find.
Mixtape - Very good card. Can copy the opponent's strongest cards if lucky, which can be game breaking.
Stick Up - Amazing card. Doubles as removal and card generation. Honestly, all the discoverable  cards are pretty good. Glowstone Gyreworm and Silver Serpent are top tier, as they instantly impact the board and are great resummons with Tess. You want to play Stick Up with another 3 or 4 mana to spare to utilize their quickdraw effects. Note that quickdraw effects aren't activated again by Tess, so cards like Trolley Problem can backfire later in the game.
Kaja'mite Creation - Excellent 2 drop that often gives you cheap removal spell.

Shell Game - One of the slowest card in the deck. Works brilliantly with Preparation.

Velarok Windblade - This card can single-handedly win matches. Tends to discover legendaries, and lets you play them for peanuts. Very strong tempo swinger.

Shadow Word: Steal - Very slow card, but very strong. Remove now and play later. Pairs well with Preparation and Sandbox Scoundrel. Excels against other control decks, where you are more or less guaranteed to grab their Titan or strongest battlecry minion.

Other cards in the deck:

Preparation - Great tempo control. Sets up big tempo swings against control, and allows you to play faster against aggro. Recall that we will be struggling to yeet cards out of our hand - this will help us to so faster.

Shadowstep - Essential. You mainly want to use it for another Tess Greymane. Marin, Gorgonzormu, Velarok and Flik Skyshiv are other great targets.

Breakdance - Essential. Similar to Shadowstep, but gives you a free rush minion for 1 extra mana.

Gear Shift - Surprisingly effective. We don't like ordinary card draw, as our hand is constantly full with cards. Gear Shift lets us cycle out e.g. our Tess Greymane and Shadowstep for later use, while digging for Reno Jackson or key removal cards.

Audio Amplifier - Essential. Being able to hold 11 rather than 10 cards is a massive improvement and enables more card generation and draw without burning cards. A feel-good card that is great in all match-ups.

Dirty Rat - Wins and loses you games. I tend to not play him early, with some exceptions. His main purpose is to decimate control decks. Works great with One Hit Wonder.

One Hit Wonder - Excellent removal. Playable on curve if needed.

Greedy Partner - 2-drop and a coin. The best coin generator in the game.

Fan of Knives - Our only normal card draw. Not essential, but works well enough against divine shields and 1 hp minions without sacrificing our health with the hero power.

Watcher of the Sun - Essential. Heal, card generation, forge (for our Ignis), and a very good bounce target. I don't like to play him without forging. Given no other options on turn 2, I tend to hero power rather than forge him or play him.

Observer of Mysteries - Tempo controller that can turn a game on its head. Sometimes, people treat him like a Doomsayer, passing on their turn. Decent bounce target.

Pozzik, Audio Engineer - Good tempo staller. Buys you time against mid range decks and other tempo decks. Playable on curve. Mill potential in control matchups.

E.T.C., Band Manager - A staple in control decks. Insert whatever is good in the meta. Gnomelia is great overall. I currently run Tony, King of Piracy as a soft counter to "curse decks", e,g. Warriors that blow up your deck, Death Knights with a million plagues, and to decks with the new mine legendary. I also run Harth Stonebrew, which can be a new win condition if you have lost Tess or need more cards.

Griftah, Trusted Vendor - Don't underestimate this guy. Gives us a much needed 4-drop that is amazing on curve with its 4/5 stats, plus a very strong 1-mana spell. Often gives you a 12 hp heal which is often the best pick. The other spells are good too. It's usually easy to pick out a card that feels great for you AND useless for your opponent.. Mill potential against control decks.

Ignis, the Eternal Flame - With few weapon removals in the meta, this card usually offers uncontested heals and removal. I find that only one forge card is needed. We can sometimes pick up new ones through our card generation is necessary. Might belong in the ETC card bank. Devastating in the late game.

Sandbox Scoundrel - Essential. Offers unreal tempo swings, Reno on 8, Marin + fantastic treasure on 8. Generally, you want to play the 5 mana dude ASAP and hang on to the 1 mana one.

Flik Skyshiv - Deletes cards on the opponent's board, hand and deck. Very strong against decks that rely on copying minions. Note that this deletes mini/gigantic versions of minions too. Great counter against the 'Discover 3 legendaries' spell from Marin, the Manager. Good bounce target.

Marin the Manager - Essential. Offers wild tempo swings. Pairs super well with Sandbox Scoundrel and Reno. Give you card draw, fatigue delay, legendaries, and card cost reduction. If you don't have Reno in hand, you almost always want to dig for him with the card draw spell. In theory, you can play turn 5 Scoundrel, turn 6 Marin + Preparation + card draw + Reno + two more cards + Breakdance for an extra 6/6 and another Marin ready for turn 7. With the summon legendary spell, always take Shoplifter Greybeard if possible. With an empty board, you will do 45 damage for 8 mana.

Zilliax Deluxe 3000 - 9 mana 4/6. Brings even more heals and stops aggression. A lifesaver that comes online a turn earlier than Reno.

Reno, Lone Ranger - Essential. There are next to no non-legendary card that we'd want to run 2 copies of anyway. In Warrior and Druid control matchups, you may want to save this for resummons of Zilliax Deluxe 3000. Pairs extremely well with Marin, as you can dig for it and play it for 0 mana. 

Tony, King of Piracy (in ETC Band Manager) - Counter to decks that fill your deck with mines, curses, bombs etc.

Gnomelia, S.A.F.E. Pilot (in ETC Band Manager) - Good removal overall. We already play a very reactive deck, so having her in the main deck is not really needed.

Harth Stonebrew (in ETC Band Manager) - Anything goes in this slot. Harth is far from necessary, but he can win you matches on his day. The Shaman deck is top tier, with Shudderwock breaking the game in your favor (multiple Renos, Tess, Marins, etc). The Warrior deck has serious OTK potential, and the Freeze Mage and Priest decks are strong but situational. The new Rogue quest legendary might be a better third option for this slot!

Card omissions

3 drops; Plagiarizarr, Beatboxer, Bounty Wrangler, Bargain Bin Buccaneer - I experimented with all of these, but found them underwhelming. 3 mana is very expensive for a minion in this deck, and it has to do A LOT to earn its stay. Gorgonzormu and Velarok Windblade are simply better, and Observer of Mysteries offers a lot more in tempo. Rusttrot Viper is currently the weak link due to lack of weapons in the meta, but if I was to swap it out, I'd go with a 2 mana minion.

Card draw - Card generation (from other classes) has anti-synergy with card draw. We can't run a plethora of both.

Excavate - Anti-synergy with our heavy focus on card generation, as you will rarely have hand space to play the final legendary. Moreover, we rely more on resummoning minions than casting spells. We want to use the bounce cards on Tess Greymane, which is arguably a stronger target than The Azerite Scorpion. As a highlander deck, we don't want to run duplicates, which makes excavation more difficult.

Zola the Gorgon - Expensive bounce. Costly tempo-wise compared to Shadowstep and Breakdance. Can't be played on Tess with a full board.

Other 5+ mana cards - The vast majority are too slow. They need to offer big tempo swings and removal to warrant a place in the deck. We don't lack value and want to be careful about sacrificing our survivability to this end. We can't re-play Rogue/Neutral cards with Tess Greymane, so there is limited value there. We will find high cost cards through our card steal.

Maestra, Mask Merchant - A lackluster tourist card overall. Extremely slow, and offers no big impact like our other 5+ mana cards. Anti-synergy with Reno and Tess. The hero cards you discover tend to be too expensive to play. When you do turn into another hero, you will "become" their class, and Tess will replay our Rogue cards which isn't what we want.

1. Match the tempo

In short, you want to stall out the game until Reno or Tess swings the game. You lack reliable AOE clear, but you are a strong tempo controller. Cards like Stick Up, Observer of Mysteries, Velrok the Deceiver, Griftah, Trusted Vendor, Pozzik, Audio Engineer, Preparation and Shadowstep are great at slowing down the tempo and keeping you alive.

2. Play good cards from other classes

When it comes to minions, you want to look for cards that are good tempo wise (e.g. removal and strong battlecries), and/or have high Tess value. The latter could be minions with taunt, lifesteal, deathrattles, high stats, rush, end of turn effects, or even Titans. Battlecries are not re-cast with Tess.

For spells, the best ones tend to be damage spells that only target enemies, like Swipe. Spells that affects 'any character' or a random character will chip away at the minions that you resummon. Cards like Lightbomb can be good clears to pick up, but Tess will kill herself when this is replayed. Which doesn't have to be bad - you get another board clear and you can use your bounce cards on other minions. But you have to adapt the game plan.

Weapons are very situational pickups. They will get re-equipped by Tess. In the August meta, there are many decks that win by chipping away at your HP pool, concede board control, and play damage from hand. Weapons don't help us prevent this. Craftman's Hammer is a great pickup however, as it gives you armor.

Hero cards are not replayed. But if you do use a hero card from another class, you become that class, and Tess will replay Rogue cards instead of cards of your new class. Even if you become Reno afterwards, you are still considered the class that you changed to. This is usually bad, as we mostly run small battlecry minions with low resummon value. That said, The Headless Horseman can be a great pickup for its endgame value.

3. Recognize your win condition against the meta decks

Tess is your win condition in a vacuum, but against many popular decks you also want to actively play to beat them. This involves targeting their key cards.

Steal and remove the right cards: Against Fatigue Warlock, Mixtape is key. If you play to steal Encroaching Insanity, you should grab an easy win. Similarly, against Control Warrior, Deepminer Brann and Boomboss Tho'grun are key targets with Dirty Rat and Shadow Word: Steal. Against Dragon Druid, taking away Puppetmaster Dorian and removing his Chia Drake's with Flik Skyshiv will slow him down immensely. Against decks that rely on Hydration Station, you want to remove taunt minions without killing them, e.g. with Amulet of Passions, Reno, or Shadow Word: Steal. Against Elemental decks, removing Lamplighter from his hand and deck is key.