You can skip 1st phase by attacking CR. I call it aggro here.
CR will teleport if aggroed (unless frozen).
CR's HP is 3/4/5/6/7 in Depth 1/2/3/4/5.
All strats here assumes you enter from the middle unless otherwise noted.
I describe the initial parity when you enter from the middle as initial parity here.
It's important on harp/pain ring aggro, electric dagger aggro and cutlass aggro.
If you want to maintain your parity after you spend 1 beat by defeating tentacles, the easiest method is to spend another 1 beat by clearing water.
Available for CR1/2.
You need to play differently on Monk/Coda, otherwise you won't be able to pick up your weapon. (Unless you have earth, but if you have earth, you can use earth strat instead).
For CR3/4/5.
You need to place the 1st bomb on the blue tile then place the 2nd bomb on a red tile.
(hokuhoku taught me this strat. Thanks!)
You can use pulse, fireball, holy water, grenade, throwing stars, weapon in holster, bat form, pain boots, glass rapier from need scroll after throw.
This video shows the optimized method of bomb aggro.
Shield
Easy.
Longsword/Spear + Glass Armor
You need to back off against 1st drum. (Kill upper one.)
If CR moved to right, you need to back off against 1st trumpet too. (Don't kill anything in this case.)
If CR moved to left, you need to back off against 1st guitar too. (Don't kill anything in this case.)
You need to kill one if you encounter 2nd piano, (You don't need to kill both.)
Dagger + Glass Armor
Basically the same as longsword/spear one, but you need to kill both if you encounter 2nd piano.
If you have glass slipeers/explorer's boots/leaping boots, you don't need to back off.
Axe, hammer, broadsword, frail, cat, whip, crossbow, blunderbuss, golden lute.
You need to move left against guitars.
You need to move right against trumpet.
You need to stay on initial parity and wait for piano/drum.
(If you aren't on initial parity, you can wait for guitar if right CR, drum if left CR. But it has only half as many chances as initial parity.)
If you have glass slipeers/explorer's boots/leaping boots, you can aggro CR with every openings. (Second half of the video)
You need to stay on initial parity and wait for piano/drum.
Also, there shouldn't be water on the tile in front of the original CR position. You need to clear that water first.
If you have glass slipeers/explorer's boots/leaping boots, you can aggro CR with every openings. (Watch the video above.)
You need to wait for drum.
As for CR4/5, you can wait for piano too.
(Why: Enemies' priorities are "weak tentacle < CR < strong tentacle", and CR have to move after tentacle in this strat.)
You need to stay on initial parity.
Also, there should be water on the tile in front of the original CR position. You shouldn't clear that water.
You can attack CR from the side.
Without water boots, normal fight is faster.
You can aggro CR by rat, grenade, pulse, holy water, blast helm and diamond's diagonal attacks.
If you have right rat, you can enter from left to ensure aggro.
Basically the same as throw strats.
You can deal damage to CR even before aggro.
This allows you to throw-bomb CR3/4 without any damage-ups.
You need to delay lunge attack in CR3/4/5.
You can use earth before clearing water.
You can't use this strat if you have axe/hammer unless you have leaping/cap/courage shovel/bat form. (If you have cap/courage shovel, you can earth -> dig-up -> earth.)
Earth meme strat is slower. Use the first one.
(Earth meme is useful when you have axe and throwing stars (/holstered dagger, but in this case you can just earth kill).)
If you use freeze spell after entering water, you automatically slide. (If you use freeze tome/scroll, you don't. Spell doesn't update "hasMoved" flag, but item does.)
Watch out for drum.
The most difficult CR strat (depends on your damage though). The video assuming upbro.
For 1st tentacle, You need to back off against piano/trumpet (piano/drum if left CR). If you have enough damege to kill 1st piano, kill the right one (left one if left CR).
Watch out for piano, they are the main reason why this strat is difficult. It's safe to aggro CR after kill the right piano (left one if left CR).
You can open the door by earthquake too.
Earthquake deals 1 damage to CR, and CR won't teleport by this damage.
You can use shove attack to drive away tentacles.
You can adjust parity by stepping back (for bomb aggro/axe aggro).
Ancalagor's great video:
You can transform before clearing water.
You can break your frost charm in trapdoor fight.
Deal 2 damage to black skeleton and push him up from the middle in trapdoor fight, and open the door, then CR can't move. In case you have ~2 damage longsword, spear, cutlass or bow.
biggiemac's nice video: