What strategy can I use to beat Isaac?

Solution 1:

As is most things in the game, your items will tell you how you should approach your strategy against Isaac. I've had bomb tears, lazers, rapid fire tears, etc. and took a very different approach each time.

General hints:

For Isaac's first form he shoots 12 radial tears. You are safe just above or below the room's center left/right (see this video). He also shoots retaliatory tears in an arc like the blood tears Monstro shoots, some might go short, some might go over you, so look for the shadows to where to dodge them. I generally just keep spinning in circles around Isaac shooting him and dodge the shadows when necessary.

His second form he shoots homing purple tears and shoots tears when hit. Again, circle around him, dodging tears when necessary.

When he starts spawning the angel babies (3rd form) that's when I usually pull out my consumables. Use your death card, my little unicorn, bombs, etc. Use em if you got em!

Also, since Isaac pauses between active attacks, it's possible to drop bombs around him with relative safety while circling him. This has an added bonus of possibly killing some of the spawned baddies he creates in his 3rd form.

Wiki link: Isaac (Boss)

Solution 2:

It's not simple to "make the fight easier", since Isaac

(and ???)

are supposed to be the hardest bosses in the whole game.

You strategy will vary wildly depending on your setup, always be prepared to adapt.

First of all, if you're still struggling to get your first Isaac kill, I suggest you to choose Isaac himself as your character, since the D6 will help you in rerolling the useless items, hopefully into something more useful.

Second, try to complete "The Doctor's Revenge!" challenge, then try to find as many secret rooms as you can. Getting the Epic fetus isn't easy, but it's basically an "I win!" item (remember to shoot with the mouse).

Try to improve your mobility, having a ton of damage and no speed will only get you killed (unless you can one-shot him or have an insane amount of health, it can happen but it completely depends on luck).

If you have a high fire rate prepare yourself for a lot of retaliation shots, a high mobility can help you here (see above).

Generally speaking High damage=Good. As it has already been suggested, in phase 3 drop all the remaining bombs you still have, those little angels can get really annoying if you let them pile up.

The radial shot can be avoided quite easily; be careful with the homing shots (the purple tears), they're fast, but if you keep moving close to the walls, they won't have enough space to turn and follow you.

As a closing suggestion, sadly, I have to tell you that you have to rely on luck: you can make the best run in the world, avoiding everything, only to arrive at Isaac finding out that your damage isn't enough, and being killed just because the fight is gonna take 20 minutes and you'll get tired and make stupid mistakes (yes, it happened to me). Keep fighting, don't lose your patience and finally you'll be victorious!

Solution 3:

I chose Cain and abused pills. Since he throws a ton of projectiles, try to use a lot of slot machines so that you can get pretty flies. Anything that will absorb projectiles will help. He doesn't really have anything that pierces, he's just a bullet hell.

Solution 4:

I recommend having the tick for this fight- at least if you're not planning on going to the chest or have mum's purse with you. It might be a pain at any other time, but that extra little chunk of health it takes off the boss' HP could be the edge that wins it for you. It also has the added bonus of giving you a red heart when you enter the boss room which might help if you're not quite up to the max.

Also try to bring as many bombs as you can, and maybe a card like the hierophant, or the lovers just in case. An active item like crack the sky, my little unicorn, or anything of that type is good for a quick damage boost if you need to catch your breath a little.

In terms of strategy, as the majority of Isaac's shots mirror your own it could be best to work slowly depending on how high your damage is. If you have a sufficiently high damage you can hug the wall and fire in short bursts rather than continuously to make things easier for yourself in terms of dodging the return shots. Staying by the wall also works for the homing shots- as long as you dodge them when they come at you, they immediately hit the wall and there's no chance of them coming back at you for a second try.

The only time when wall hugging might not be the best option is during Isaac's third phase, as the angel babies can easily trap you in a corner and pelt you with shots until you're either dead or nearly dead. As long as you keep moving in wide sweeps around Isaac and make sure to avoid his beams of light, you should be ok.