THIS is where a reliable tactic comes into play.
The pegasi + archer will have a serious addition of Hero's Bane units. This won't be the case where you have 1-2 stupid elves, oh no. The AI will be able to put down 3-5 of these in turns many times. So this is serious. The enemy also have a limited amount of mediocre legendary cards,
The initial problem is something else though: archer towers. They can hit your Heros, and they can hit hard. They must be disposed early. But try to hold direct damage for later when possible - of course not at all cost.
Second problem is the first wave of pegasi - they aren't that great in number, and you can survive here quit long even with wrong tactic.
Third problem will be the constant Hero's Bane, what means no matter how hanky your units are, you will be damaged, and in the end bleed to death.
The enemy has like a hundred cards, so there's no hope with a bash'em strategy to win.
Blizzard is common, Petrify comes reliably, and some Fireballs is also in the basket.
The key to win
Only a specific condition can make you win: Reckless Shot (eg. Sylvi Ranger). Or better: Yumi (halfblood legendary).
Let's assume you'll use the cheaper solution and bring something with Reckless Shot. Due to game-mechanics this is physical damage to self, so with Blessing: Armour can be countered. If you are lucky and have Epic version of it, only 2 of it you'll need to compensate for the 5 HP damage. If you are unlucky and poor, you'll need 3.
Because of Blizzard you better have Blessing: Resistance too. Better wait for it to add imediatelly (once B:A is ready to be cast it'll avaiable each turn, while B:R will have a 2 turn cycle).
NOTE: on a creature only 5 buffs can be - at least no more is shown. You must calculate your blessing in the face of this.
NOTE 2: Blessing: Life can extend an improperly buffed Reckless Shot unit for 1 more turn.
NOTE 3: Decay cast on the Reckless Shot unit further incrise its usefullness, making practically any unit of the AI never survive its first turn. Not absultely necessary though.
You MUST talk and cooperate with your team to successfully carry out this strategy! Hold your extra buffs and Key Units in case a Fireball shots down your buffed one.
2*Healer, 1 Mage, 1 more
Reason: The Healers can cooperate by bringing 3 Blessing: Armor each, drasticly incrising the chance to perform a successul raid.
One of the Healers will be the Key Person, who'll bring 3 of the Reckless Shot units, 3 Armor, 1-2 Dispel (in case the Key Unit gets petrified). The remaining units in his/her deck shall be Desperate Soul (no real alternative), 1-2 Blessing: Resistance, some longbow snipers / tanks. 15 cards deck to make it reliable. Sanctuary is not top priority, can be left out. Secondary Healers of course advised to bring it with high priority.
The others shall bring units who can protect the team's archers, and the Heros themselves. Preferably high HP, ability of disposing pegasi, and one-hit kill against the enemy archers (3+ damage). These units main purpose is to hold the lines until The Tactic is performed (at which point things will be much more easy) and dispose the initial archer-towers. They will be the ones killing the enemy Boss too at the end, preventing Sudden Death killing the team whose HP got lowered by Hero's Bane. ca 20 cards deck suggested.
You MUST have enchanted equipment at this point, King Set pieces all. Hero HP is important for this.
The Mage is suggested to bring Petrify and Fog of War. Fog of War can be tricky to use, best telling when you want to cast it, so the team can put down fresh units AFTER its use (so they won't be effected). Dispelling the effect Fog of War from your units might also worth a card at the right moment.
Petrify is not your enemy! It can create an excelent meat-shield for you.
If you Dispel Petrify, the unit under the effect will loose the 10 HP gained from the spell, possibly making it die. Keep this in mind.
Archers of 3-4 damage + longbow (+ sniper), centaur guerilla leaders (high base dmg, hit and run strenghtened with charge) are good units.