I figured we could list a few strategies to make this stage easier and more fluid. So here are some, along with the description of the stage. Feel free to add or correct me.
In order you will be facing this:
Starting Point (1) -> Seshya's Room (2)
-> Jelly + Crystal Room (3) -> Trap + Pirate Room (4) -> Illusionary Beast's Room (5)
-> Turtle King + Shark Room (6)
-> Tarask (7)
1. Starting Point:
---Very simple, you can get the stage quest that neats you around 12% exp from the left crystal. Just go upwards to fight a few jellys and break the right door to start the stage.
Clear the Slimes and break the pots to open the door
2. Seshya's Room
---Once you walk the hallway, she will pass by you until the center; there will be a lot of those 1 zillion hp snake pots, destroy them to make Seshya show up. You can stay on the corners to avoid being hit at all, but that will make the fight longer. Just be carefull not to get yourself killed when she slides the area, her other 2 attacks won't kill you, so you can take your time to hit her head. It can take some time, but this shouldn't be a problem.
Break the pots to make Seshya come
Same strategies, Seshya can't reach you at this place
3. Jelly + Crystal Room
---After the snake, you will reach a T intersection. Carefull with the falling tablets, they don't hurt, but if you are low on health, you will have wasted a precious life. Your goal is to hit the big crystal in each side. Once you hit them, the 2 smaller ones will start to attack with 8 direction beams (around 50 dmg only) and throw a poison cloud. Some poisonous and big jellys are going to spawn, and they need to be killed to proceed. Once you are done with both sides, return to the center and proceed up.
Hit the biggest crystal to spawn slimes, but wait for the smaller ones move to the corners
4. Trap + Pirate Room
---Same layout, but this time, each room will have a glowing tile on the center, where all party members must step on. This will make 4 crystals to appear, all of them with traps; so far I've seen 5 types*: fury of land trap (will leave you at 0 hp, but won't kill or kd you), imobilization trap (explosion on center and freezing beams around), bolt trap (series of lightnings that will kd you, therefore they CAN kill you), null trap (nothing happens) and the pirate trap (a group of pirates will spawn). You are aiming for the last one. Once you kill the pirates, a message will appear, and you can repeat the process with the other room. Uppon clearing the 2 rooms, you can proceed up, but once you step on the hallway, a 3rd group of pirates will spawn behind you. Dispose of them to continue.
* There's a 6th kind, pillar of abyss trap, which does hurt, but you can dash around to avoid most of the hits. Don't lie down or it will possibly kill you. Thanks to Dewedi for the tip!
All party members must step on the center. Then you must choose 1 crystal, hoping for it to be a pirate trap
5. Illusionary Beast's Room
---This room is a joke. Might be a bug, but this boss has very little HP. It's possible that Siege's Destruction Fist can 1-hit KO him. Walls will fall around modifying the layout of the room, but the boss will be dead before that. Proceed up for a raid like room.
6. Turtle King + Shark Room
--- This room is my favourite. Again, all party members must step in the glowing tile to start it. First wave will be made of several mini-turtles (down attack ones), 4 turtle kings and 2 giant turtle kings (4-2 boss). They will come in waves, are are slow enough to be dodged. Extreme care with the giant turtle kings and their rolling attacks. There's plenty of space anyway. Once they are dead, step again on the tile, and this time you will have a shark wave, with several shamurlocks and two 4-9 bosses. They are slow as well, but you should avoid corners because it's easy to get bodyblocked by them. Once they are dead, the door to Tarask's Room will be open. Heal up, cast any buff if you want to and go.
Turtle King waves
7. Tarask's Room
--- Tarask is a Hydra type boss, with 5 heads, but he doesn't move at all, so there are safe spots behind him, like top left (behind yellow head) and right. Each head has a special attack: a stomp, a mad fury of land type, a really long freezing beam, a flare tornado and a poisonous gas, I didn't memorize which head has each attack in particular, but the yellow head you will hide behind has the stomp.
---The central head, is the head linked to HP bar; if you hit that, his HP will slowly decrease, but you probably don't want to do that at early levels, because of those nasty attacks. Also, every head has a breath attack that will kill you, unles you have a healer. It's really easy to notice because the head will charge for this attack, and gas will gather on the mouth; so if you see that, run as fast as you can behind him. If you are hit, DO NOT GET UP, healer will go for you and save you with emergency heal or sunlight.
--- Since you won't be hitting the central head, keep pummeling the 2 lateral heads. They have no life bar, and neither his main HP bar will decrease, but they will die eventually, depleting part of his HP. You will probably manage to kill those 2 lateral heads, then you can proceed to the central (being careful not to get hit by other attacks). The 2 heads you killed will regenerate from time to time, so just repeat the process. He will be really easy to beat, it will just take longer. And that's it! You beat 4-10 boss!
Tarask overlook, where to stand and what to damage
I'll keep updating this as people add coments, and I'll try to screen each room. I always forget to do so because I am really focused healing everyone. Hope this can help people trying to beat him. By the way, I blurred other people's names because I forgot to ask them if they wanted it to be public, and because I couldn't reach Tarask's room by my own. I hope that is ok.