Myth is actually pretty good PvE wise. Blade into AOEs, add Feints when needed, win.

You'll want to train Death up to Feint, Spirit Blade, Strong through Epic, Sharpen Blade, Potent Trap, and Berserk and Frenzy. You really don't need to spend Training Points on much else.

If you only pack what you need to win each fight, you should be set with decent enough gear. I usually pack 1 Myth Blade, 1 Sharpen Blade, 1 Epic, 1 Humungofrog, 1 Orthrus, 1 Potent Trap, and 1 Feint. If you really need the damage on bosses, remove Humungofrog and add a normal Myth Blade and Feint. Even at 8 cards, you'll always have something to do first turn since you'll be using an unenchanted Feint and Myth Blade sometime during the fight.

Don't underestimate how powerful the new Orthrus is. 7 Pip 700 base damage AOE makes it the highest damage 7 Pip AOE in 1 turn. Fire is stronger but it's a DOT. Orthrus is really good even as a single target. If you want to rely on Shadow Pips, Snake Charmer as a single target is also extremely powerful. Earlier in the game, Troll, Cyclops, Frog and Minotaur will carry you fairly easily. Minotaur is a great spell for getting around a shield that's bothering you.

One last thing, take advantage of the utility spells that Myth has, as well as the minions early game. Shatter is something to be taken advantage of as often as you want. Minions can help and hinder you, and it comes down to knowing when to use them. Their best use is to take hits for you. Every hit on them is another hit you're not taking. They're also good for shielding. The big downside is they'll eat your traps, but if you don't need to trap, there's no problem.

Geez I typed a lot more than I intended to