We've started a new campaign, and I feel like killing a single hero over and over again is a dumb but rewarding strategy for OL.

Basically:

-You get a card for each KO

-When a character is revived, he got *almost* no Stamina and minimum HP - so why not kill an easy prey again

-Heroes would lose and action

Is there anything heroes can do to counteract that? I feel this makes it less interesting tactically, but I would have to do suboptimal choices if I decide not to go for it.

It is a great strategy for the overlord to pursue as long as he can keep getting cards from it. Before getting to hero countering tactics, let me point out some gameplay features which make it beneficial for the overlord to share the love:

-Threat tokens. The OL can take a threat token instead of an OL card once per quest per hero . That is, there are up to 4 threat tokens to gain this way per quest (in a 4 hero game) if he KOs all the heroes, but he'll only get 1 per quest if he repeatedly KOs the same hero.

-Tainted cards. Heroes become tainted when they are first KO during a quest. After becoming tainted, a hero can no longer revive or heal another hero while said hero is KO. If the OL is repeatedly KOing one hero, that's the only hero who will be tainted, which isn't really a problem (he just can't stand up). If the OL shifts his attention to the other members of the party, he can cripple the whole team (which is how he wins most quests in Mists of Bilehall).

As far as countermeasures, the heroes absolutely have some. My favorites are:

-Health and Stamina potions. Instead of performing a revive action, a hero can use a health potion to heal a fallen comrade- he'll regain all of his damage. He can also use a stamina potion after that hero is up to restore all of his fatigue.

-Revive+Rest. After a hero has been revived (or healed by some other means) he gets to take his turn as normal. One of his actions (assuming he's out of harm's way) can be to rest. Next round, he'll have all of his fatigue to spend. If he stands himself up, this takes a lot longer to do.

-Knight "Defend". The knight has a great skill that lets him take attacks instead of an adjacent hero. Keep the knight next to your weakling and he has an extra layer of protection.

-Bait. Give the overlord a better target. Whether that is a hero who is in a position to deal damage to an important monster, or simply putting heroes between the monsters and the weak hero as human shields.

Also, a hero which is knocked out doesn't have to stand up during his turn and the other group members don't have to revive him. The other heroes can maybe lure the monsters away from their fallen comrade or kill them first before reviving him. This way the OL cannot get an easy card every turn.

In addition to that there are some items which improve the process of reviving a hero. Phoenix Pendant (SoN) heals 3 additional wounds when being revived or standing up, Merciful Boots (LotW) heals 2 fatigue for the revived hero, and there is a relic armor which allows you to teleport the token to your position.

In addition to that there are heroes which have skills to stand up or revive easier or with boni (Rendiel, Orkrell) and classes skills that provide boni (Berserker)