Turn them Away
First and foremost we want to have people attack, but not us. This is easily solved through two means; pillowfort and fog effects.
Employ some pillowfort in the deck, and use cards like the basic Propaganda, Ghostly Prison, the Archon of Absolution, and the technically pillowfort but actually “rattelsnake” effects of Marchesa's Decree and Teysa, Envoy of Ghosts. All of these can cost the opponent resources they may not want to pay.
If other players are still swinging into you, make them pay for it. Outside of cards like Ghostly Prison and Propanada, we can use fog effects and other means of turning the aside.
Note: Because Connive / Concoct are considered to have an odd mana cost of 4+5=9, I believe either side can be cast with Yennett. Below are the rules for split cards, current as of Crimson Vow. However, please ask your local judge if you have one for clarity, and I am not one XP
The comprehensive rules PDF provided by Wizards of the Coast here:
https://magic.wizards.com/en/rules
For reference from the Comprehensive Rules:
709. Split Cards
709.1. Split cards have two card faces on a single card. The back of a split card is the normal Magic
card back.
709.2. Although split cards have two castable halves, each split card is only one card. For example, a
player who has drawn or discarded a split card has drawn or discarded one card, not two.
709.3. A player chooses which half of a split card they are casting before putting it onto the stack.
709.3a Only the chosen half is evaluated to see if it can be cast. Only that half is considered to be
put onto the stack.
709.3b While on the stack, only the characteristics of the half being cast exist. The other half’s
characteristics are treated as though they didn’t exist.
709.3c An effect may create a copy of a split card and allow a player to cast the copy. That copy
retains the characteristics of the two halves separated into the same two halves as the original
card. (See rule 707.12.)
709.4. In every zone except the stack, the characteristics of a split card are those of its two halves
combined. This is a change from previous rules.
709.4a Each split card has two names. If an effect instructs a player to choose a card name and the
player wants to choose a split card’s name, the player must choose one of those names and not
both. An object has the chosen name if one of its names is the chosen name.
709.4b The mana cost of a split card is the combined mana costs of its two halves. A split card’s
colors and mana value are determined from its combined mana cost. An effect that refers
specifically to the symbols in a split card’s mana cost sees the separate symbols rather than the
whole mana cost.
Example: Assault//Battery’s mana cost is {3}{R}{G}. It’s a red and green card with a
mana value of 5. If you cast Assault, the resulting spell is a red spell with a mana value
of 1.
Example: Fire//Ice’s mana cost is {2}{U}{R}. It has the same mana cost as Steam
Augury, but an effect such as that of Jegantha, the Wellspring sees that it contains the
mana symbol {1} twice.
709.4c A split card has each card type specified on either of its halves and each ability in the text
box of each half.
709.4d The characteristics of a fused split spell on the stack are also those of its two halves
combined (see rule 702.102, “Fuse”).
These effects include Darkness, Dawn Charm, Batwing Brume, Inkshield, Comeuppance and Selfless Squire. Darkness is the only card here that ONLY stops damage, but the other cards have other benefits. Dawn charm is also a counterspell to protect yourself or protection for a creature. Batwing Brume can take token player and make them have serious regrets by draining their life. And Inkshield, while expensive, can turn the tables by giving you the crack back damage you need to end a game, and Selfless Squire is similar. Comeuppance is the only card here that can immediately crack back against things like Chandra's Ignition or Aetherflux Reservoir.
Make 'Em Stray
While I don't use Goad effects in this build, I do use something similar in the cards Gideon Jura, Siren's Call, Imaginary Threats, Bident of Thassa, and Shipwreck Singer. Gideon Jura, Bident of Thassa, and Shipwreck Singer can be used multiple times is a game, making them very useful, while the one time Siren's Call and Imaginary Threats, assuming you don't recur them, can clear a path forward for your own creatures.
Each can force attacks into bad conditions, or just when your opponent's don't want to do anything but sit around. With these we also don't force EVERYONE to attack every turn, so we don't generate the focus of the whole table as if we used something like Goad. This allows us to make deals and be “helpful”.
Likewise, cards like Sudden Spoiling and Polymorphist's Jest can make all of your opponents' scary big creatures be easily crushed by your own during an attack, or when someone else attacks. They can even turn the tides for someone you want to help! Remember that your opponents are also potential lines of play to weaponize against other opponents.
Into the Fray
Of course, being a deck built around combat, we get to swing with our own creatures. Yennet herself is hard to block her abilities of Flying and Menace, but we have other creatures that will gain us an advantage on the swing.
Varragoth, Bloodsky Sire has deathtouch, and we get a tutor out the attack even if someone wants to trade with it on the attack, which helps Yennett's triggered ability. Tymna rewards us with even more cards if we are successful in combat. Likewise, Breena, the Demagogue rewards us for both attacking and keeping life totals even, and when opponents' do it themselves or are forced to. Cemetery Illuminator helps us with the top of our deck and Yuriko, the Tiger's Shadow does the usual life drain and can potentially help us use other ETB effect later, like Karmic Guide or Angel of the Dire Hour.
Some other cards that help us that trigger in combat are Sword of Hearth and Home, Explorer's Scope, and Sword of the Animist. All of them can get lands from the deck or the top of the library out of the way to reduce whiffs with Yennet, and the Sword can trigger more ETBs AFTER combat, which is very good for the deck's strategy and essentially untaps one of our creatures.
Better To Prey
This isn't a passive deck. We want to get in there and smack some faces. However, sometimes we will be behind or targeted down, and we need an opening to finish up the job if our machinations didn't work out so well.
First up we have Reins of Power, which can trade our field away for an opponent's. This is especially good against someone who just used a card like Cyclonic Rift, Winds of Abandon, or Settle the Wreckage, and allows us a potential win or stabilization. It can also be a really expensive Fog effect. Akroma's Will is a great combat-oriented finisher, board protector, and game-ender. It being Instant speed is just perfect for anything we want to accomplish. With some Surveil and Scry, if we know Magister Sphinx is on top of the deck and attack with Yennett, we can change the calculus and take someone out of the game with a surprise lethal attack after it enters the battlefield. With enough creatures with enough keyword abilities Akroma, Vision of Ixidor will be able to pump our team into a lethal range quickly. This is particularly deadly in tandem with Odric, Lunarch Marshal, and effective with other cards like Angelic Skirmisher or the before mentioned Akroma's Will.
The maybe section has some other cards you can include in this build, and there are many other cards not mentioned, like Cunning Rhetoric or any Goad card like Bloodthirsty Blade. You could even add a blink package besides Sword of Hearth and Home if you want. Yennett is a very open ended commander and will lend herself to a number of different styles.
