You can stack different status effects-- like he can be poisoned, AND on fire, AND cursed all at the same time. Solo is a little harder because the more time you take to chuck vials, the less time you're actively hitting him. Keep in mind that some vials last longer than others-- so don't throw poison first. It lasts the least amount of time. Throw Curse, then Shock/Stun/Fire (whichever you choose), and then poison last.

You want to be in his face meleeing him, but unlike in group play where you can just go crazy, you have to be mindful of the swarm of little jellies. You want to lay into him as much as possible, but at the same time you want to avoid damage when you can. Shield Bump enemies in the middle of combos (Personally, I stop one attack short of a "finisher", making shielding instant), and that should offset some of the damage you end up taking.

When you use vials is more important, as well. Curse is great in the first phase, but is far more important in the second-- so if you start the Jelly King with only 1 vial, save it for the second. This is because he heals more health per tick in second phase, and it's harder to be having constant DPS on him-- so the extra chunk Curse gives sets you that much further ahead. Fire is a better pick for first phase, because he won't go immune to damage, meaning every tick counts. Stun and shock are useful in either phase (I like using them in second phase personally-- since it makes him choke up on his spin), and so is poison-- but if you're solo you need to be choosy about which vials you bring.

When he hits the second phase (marked by him going pink, and spinning all the way around the room), make some space between you, and him. Use that time to kite a little and pop a pill in order to fill your health up, and then start a charge attack with your main melee weapon. Remember: Jelly King ALWAYS spins in a COUNTER CLOCKWISE manner, starting at 3-o'clock. If you don't know what that means, look at a clock. He'll turn pink, then head in the direction of "3" on a clock face, then go through 2, 1, 12, 11, 10, 9, 8, 7, 6, 5, 4. With this knowledge you can predict where his spin ends, meaning where you kind of want to head in order to plant that charge attack right in his face.

Sidetip: Don't wait RIGHT where he's going to finish-- as he may spin into you and cancel your charge attack. Always keep in motion, and head towards the general area-- that way little jellies can't smack you in the face either.

Between "angry spins", there's about a 1-2 second delay, and then the Jelly King will do one attack, delay for another 1-2 seconds, and then "angry spin" again. My "rotation" is to let the charge attack go, and then toss a couple vials. By the time attack buffering on vials is done, he'll have done a regular attack, so I lay a full combo into him, then shield. You have time for one combo between regular attack and arena spin, so putting up your shield means you won't take damage, and he pushes you away (giving you breathing room)

What tier 4 bombs are good on Jelly King runs?

Nightblade / Silent Nightblade / Acheron line of weapons will kill the jelly king really fast... much faster than Gran Faust imo. But Gran Faust has it's advantages against groups of enemies. For vial use you can just run up to him and use them in melee range to ensure hits... but try not to use vials after he has turned purple for 4-5s because he'll most likely turn pink and be invuln by the time the vial hits. When he spins and turns pink try to stay in front of the direction that he's spinning towards, that way when he turns purple again you can run up to him and deal dmg without being swarmed by the smaller jellies.

Communication is also key... make sure everyone in your party understands that attacking the JK and ignoring the smaller jellies is the attack plan.

In the palace, but not the Royal Jelly fight itself, there is no question that fire is the best bomb, and the blast bomb series is always useful especially if you learn how to place it to knock the enemy back to specific spot. I use a Master Blast Bomb (UV +med dmg to slime) while my mate uses a fiery atomizer. She sets the room on fire and I knock and stragglers back into the flames. I call this the "burn and boom." It's a quick way to dispatch of slime.

Ice bombs are less effective in the royal jelly palace. There are a lot of smaller rooms with a lot of jelly cubes in them. Freezing the jellies in place doesn't stop them from attacking you, so can still get hurt waiting for them to thaw. Ice can work, but it's slow and requires patience that most people lack. Fire ticks, on the other hand, kill them very quickly.