bool move_respawns       = false;

        move_respawns   =  strip_tag(spec, "move_respawns");

                case MSGCH_MONSTER_DAMAGE:

                // If a monster-damage message ends with '!' it's a
                // death message, otherwise it's an examination message
                // and should be skipped.
                case MSGCH_MONSTER_DAMAGE:
                    if (msg[msg.length() - 1] != '!')
                        continue;
                    break;

            int idx = dgn_place_monster(spec, 0, pos, false, true);

            int idx = dgn_place_monster(spec, you.your_level, pos, false,
                                        true);

                idx = dgn_place_monster(spec, 0, pos, false, true);

                idx = dgn_place_monster(spec, you.your_level, pos, false,
                                        true);

                if (move_respawns)
                    monster_teleport(&menv[idx], true, true);

            arena::faction_a.won = false;
            arena::faction_b.won = false;

If you want a *specific* set of monsters to fight each other endlessly,
you can use the "respawn" tag, which will cause the initally placed
monsters to be replaced when they die.  For example,
    crawl -arena "respawn rat v rat"

will make it so that when one rat dies another takes it's place,
resulting in an endless fight between two rats.

If the arena has lots of monsters it might take a few second before it

If the arena has lots of monsters it might take a few seconds before it

      It also controls what type of monster "random" places, assuming
      that "random_uniques" isn't used.

* move_respawns: Moves respawned monsters to a new, random location as
      soon as they're placed, to avoid monsters clumping up in a massive
      brawl at the center of the arena.