Create your own artifacts!

Here are some of my ideas:

Vampire Amulet (presumably, major)
At the start of the battle, a random unit from the friendly creatures receives the "Vampirism" spell for 10 turns, allowing it to convert up to 50% of the damage dealt into health (i.e., like the vampires' ability). If the army contains both ranged and melee units, Vampirism cannot be applied to ranged units. If there are only ranged units, it is applied to a random one. The spell is cast in the usual way and can be dispelled. All vampires in the hero's army receive +2 to attack and defense.

Goblin Shaman's Rattle (left hand, presumably, major)
Gives the hero an active, non-magical ability called "Magic Disruption," which works on the same principle as the Goblin Shaman's ability, consumes only 50% of the hero's initiative, does not require mana, and lasts until the first cast of a targeted spell/enemy hero. The strength of the casting hero is determined by the same formula as the strength of the enemy hero. All goblins in the hero's army receive +1 to morale.

*** (name in development, helmet, relic)
All friendly creatures in defense mode gain the "Endless Retaliation" ability. (If the hero has the "Readiness" skill, creatures do not gain "Endless Retaliation" when given the "Defense" order, but instead receive an additional +5 to defense. Creatures that already have the "Endless Retaliation" ability built-in also receive +5 to defense.)

Sword of Fury (presumably, major)
If a friendly creature attacks, it receives +3 to attack. If it defends or waits, it receives -3 to attack. For the next similar action, it receives an additional +/- 2 to attack, and for the 3rd and subsequent actions, +/- 1. If the sequence of identical actions (attack/defense or wait) is broken, the creature loses all bonuses and penalties to attack, and everything starts over. Movement without attacking does not affect the increase/decrease in attack. Orcs lose twice as much attack when waiting, and dwarves do not lose attack when defending, and any accumulated attack bonuses are not reset.

Banner of the Dreadful Leader (presumably, major, not sure where it would best fit)

The hero forces creatures to fight much more effectively, but under the threat of their own death, and as the chances of victory decrease, the creatures' morale drops, and eventually, they may betray the hero.

Creatures receive +5 to attack and +1 to initiative. At the same time, they also receive some penalties:

75-100% of the creatures in the unit (from the number that was at the beginning of the battle): -1 to morale
50-74% of the creatures in the unit: -2 to morale
30-50% of the creatures in the unit: -3 to morale
Less than 30%: creatures of level 1-3 inclusive - betrayal (like goblins, they switch to the enemy side). Level 4 and 5 -5 to morale, level 6 and 7 -3 to morale.

Undead creatures are immune to any effect of the artifact.