What class are you playing anyway? My post Moon Lord experience (so nothing from Tavernkeep yet, only other endgame stuff) turned out this way...
Arena - just a long plain, no traps, clean and easy. Crystal Stand in the mid.
Melee (tried beating event with him first) in Solar Flare armor with wings, boots, ankh, shell, warrior and destroyer emblems (all warding) using Terrarian, Eruption, Meowmere, Star Wrath and 3 stardust summons plus some ML sentry while buffed up with every single possible melee buff/potion - NO LUCK. At Betsy ofc (wave 7). Waves 1-6 are easy, but with Betsy I was either able to try killing her or preventing monsters below from eating Eternia Crystal alive. Didn't even manage to kill her once after crystal got destroyed and started the fail animation (she was low tho). Classical melee build just seems to have lower DPS and so-so AOE options. Didn't actually try flying around in the saucer and switching to more DPS accessories (or even reforging out of "warding", but it's kinda uncool). Hm. Might have actually worked, I'll give it a try later.
So I gave up and tried Ranger. He's kinda my least favorite one tho, but I'm pretty aware of his potential. Vortex set, SDMG, just Endless Musket Pouch, no buffs (except food, pies are always on). Wings, boots, ninja gear, shell, ankh, sniper scope (all warding). Rainbow Crystal and 2x Stardust Cells (Bewitching Table used) I understand luminite bullets would have been better, as well as DPS trinkets, but whatever. Waves 1-6 killed easily without moving, no matter in or out of stealth mode. Betsy died after crystal got destroyed. Over. So with just a little more tweaking (or mind you - buffs!) no-etherian-mana I'm sure Ranger will easily kill em all.
Next was Mage. Mostly used Lunar Flare on the first try, also checked Blaze/Arcanum, turned out Prism is kinda laziest one mostly due to having huge range with AOE built-in so no moving required. No buffs except food, Mana Regeneration Potion, Crystal Ball and Bewitching Table was too lazy to move to get nebula boosters, only picked them before Betsy spawn and on. Wings, boots, ankh, shell, ninja gear, destroyer emblem. Sentry, 2 Minions. Betsy died on the very first try. That was the first win on this event for me. I think reasons are that Mage has very high DPS and a sexy AOE. So I was mostly shooting/dodging Betsy and when I saw usual wave monsters getting too close to the crystal I just turned on them from whatever angle/position for a couple of seconds and wiped them to hell. And yes, ranged with piercing bullets could do that almost as easy by landing on either side and shooting horizontally for a couple of seconds, I do realize this now.
Summoner. I love this class, it's so AFKish 
Stardust armor, wings, boots, ankh, shell, ninja gear, Papyrus Scarab (all warding). Of course, as minions don't change their damage after the summoning I do switch some gear when I call them. Hercules Beetle, Summoner/Avenger emblems, Necromantic Scroll (all menacing) go instead non-damaging trinkets in the process of summoning. Also I sit on a Cute Fishron in some pond/honey reservoir. Long Stardust Dragon and a single Stardust Cell, my usual all-round party. Food, Bewitching Table. Did use Summoning Potion a couple of times, but they run out so fast... meh, too lazy for that. Rainbow Crystal/Lunar Portal refreshed on one side, Stardust Guardian on the other (might skip him actually). AFK kill waves 1-5. You might get hit for a couple of hundreds HP, but it'll regenerate to full pretty fast anyway. Wave 6 generally requires some dodging (and in unlucky cases even shooting not to lose too much crystal HP), dragon doesn't react fast enough to prevent damage from ranged and divers. Betsy died after crystal was destroyed. Then I realized that summoner might use some weapon as well. Last Prism (did use Mana Regeneration Potions and Crystal Ball with it then) or Star Wrath (might sharpen it then) did well in killing minor enemies. Not as devastating as in Mage's hands, yet acceptable. Addition of possibility to order your minions to focus on some single target is pretty neat. Did some tries, successfully for the most part. So Summoner works quite well there for me. Might be slightly luck dependent (dragon is quite silly, yeah), but kinda same overall DPS/efficiency as Mage.
Then I returned to Warrior (melee). Nothing new,no enough DPS. As I had a ton of Defender Medals I decided to try it the intended way. Valhalla Knight armor, Ballista Staff, wings, boots, ankh, shell, ninja gear, destroyer emblem (all warding), Terrarian only, two-segment dragon, food, Bewitching Table, Sharpening Station. Could also use up to 4 (5 with one of those new accessories) Rainbow Crystals/Lunar Portals, but thought I'd give it a try this way. Easy peasy. Ended up not even spending wave 6 mana, stored it in a chest dunno what for. On Betsy only focused her, buffed ballistas do wonders vs usual monsters there. Bonus is awesome as well, very self-consistent - get hurt by Betsy from time to time - ballistas wreak havoc below even better (like they didn't do that good enough already) - you regen health back extremely fast. Sweet.
