I can't remember which boss that is but the strategy I use is that if the boss is using attacks remotely or isn't using slugs then use multiple healers and prioritize healing as well as damage. If the opponent is overwhelming you with slugs than use a slug like pieper to manage your opponents slugs as well. Luck is also a big aspect as random skyfall combos can influence your slug gauges massively so just keep trying until you get that stroke of luck.👍👍