Homebrew Creature: The Bog Lurker

[kind oasis]

It's been a while since I've tried my hand at homebrewing, so I've decided to try my hand on a boss monster to be fought at around levels 5-10.

The mire in the bog conceals death in the form of choking vines and underwater thorns. Locals who once skillfully navigated the dark swamp now disappear by the day, leaving no trace as to where they've gone. The party have been tasked in investigating the disappearances, but if they lurk too close to the monster's brood, they may find themselves pulled down to the depths of a watery tomb.

I'd like to ask for feedback on this creature. Thanks.

[normal yoke]

Looks like an awsome monster! I'd consider lowering the AC a smidge, since range is really the only way to get at it. I realize its a CR9, but its got some intense offensive options up close, and range (with a max to hit of 25) will only hit 10% of the time with that thrashing vines feature - so it may be a bit OP. It looks like a lot of fun for roleplay!

Alternatively, you could also make thrashing vines only effective when the target is 30-60, since it has blindsight beyond 60ft...that way a target could stay outside of 60ft and have a range to hit (max 25) of 40%.

In any case - really cool job on this. I like.

[kind oasis]

15 sound large until you remember that adventurers at that CR's pay grade have something like +9 to hit, so they'll hit 70% of the time, which is actually above average.

360 is based on an average of 90 damage per round, which is the average damage of three subclassless martials with GWM or SS attacking it twice

So it's meant to survive four rounds

[kind oasis]

The point of the monster's ranges and features are that you cannot snipe away at it.

Otherwise, it would be relatively easy to simply kite away at it.

You have to get in close to deal damage, and that means putting yourself at risk

Range is already strong as it is in 5e, I'm not giving the archers and spellcasters a free pass.

[kind oasis]

Also, the actual chance assuming normal roll is .70 * .75 = 52.5%, not sure how you got 10%. Ranged characters at 9th level can have a +5 in their key ability score and +4 proficiency, for a max of 29.

If a 5-8th level character, the chance is .65 * .75 = 49%, a little worse but still statistically not that bad. Disadvantage would drop it to 31%, which is abysmal but not as bad as the 10% you say.

A boss monster that can be cheesed with ranged options is not really a boss fight.

The boss has to actually challenge the players to be considered a boss.

[normal yoke]

Maybe I hacked my math! Love the monster!

[unique rose]

I think you accidentally reversed the thrashing vines so that after hitting range needs to roll a 1-5 to confirm success, rather then the actual stated of monster avoids damage on a followup roll of 1-5 ( .25 * .6 = 15%)