#RookieDM Problems

As a personal goal I've been working on DMing a D&D campaign for the first time. I got tired of looking at the basic monster manual stuff and wanted to make something totally RAD for the Arc closer. I love Metal Gear's trend of 'Quirky Super Soldier Squads' and wanted to design some as recurring villains for the party.

And I LOVED it! Making your player characters, you're always aware of the limitations...where rule of cool won't fly with mechanics. Designing bosses, it's like...you got some parameters sure but go do those cool things you always wanted to!

So I put in tonnes of stuff I liked...with a mindset to be VERY tentative about not wanting to absolutely slaughter the party. I wanted it to be a challenge though and a significant threat. I wanted to incorporate some stuff from games I liked like FFXIV so I put in a multiple-phase mechanic, two different fighting styles, and CRUCIALLY, an overarching mechanic to the fight that would be lethal if ignored. I felt really proud and super-hyped with what I'd made. I couldn't wait for the party to fight her.

Except things went unexpectedly wrong. The crucial mechanic basically revolved around party members being compelled to fight ONE other party member chosen at random by the dice, with them getting a nice reward on their next attack's damage if they did, as well as alleviating a progressive debuff. If they ignore the debuff too long they basically KO themselves and come back as rage zombies.

Two party members get the same target for their mechanic. Said target PC ran forward and went invisible...giving them no outlet to dispel their mechanic for like...3 turns, by which point the fight was turning against the party thanks to the debuffs. They did get close, knocking the boss down to 38/140 HP but it was a wipe and this was a real downer for some party members (and me a fair bit).

Now, I'm tearing myself up a bit over how I could do this better next time, whether it's fine or whether I need to make more changes. I had planned to do this with potentially FIVE other unique bosses but as I've not done this much I'm pretty worried that I'll floor them again.

TLDR:

RookieDM tries something they think is rad, does not know their own power, wipes the party. Deep contemplating is needed for improvement as a GM.

The boss herself. Names are inconsistent because I hadn't settled on a name. The Quirky Super Soldier Squad I have in mind is built along the lines of different facets of death. This one was for Violent Deaths, those of soldiers on the battlefield. Again owing to my love of Metal Gear, I wanted a good old hand-to-hand combat which is the basis of the two attack modes.

The mechanic that caused all the problems. I'd like to think it was reasonably foreshadowed but I know some of the players hadn't really clocked what they might be walking into. DC checks are high but that's because I wanted this to be more of a MECHANIC than a simple "save and ignore it" situation. Blacked out bits are player names.