Krumblor

To unlock Krumblor you are required to purchase the heavenly upgrade “How to Bake Your Dragon”, costing 9 heavenly chips. Krumblor can then be purchased as the upgrade “A crumbly egg” after having baked 1 million cookies during that ascension, and it only costs 25 cookies, at which point Krumblor will appear as an egg in the bottom left corner of the game and evolve into a dragon as you sacrifice cookies and buildings to him.

When you first get Krumblor he will not give any benefit, as he is still an egg. You need to pay a total of 15 million cookies to hatch him, at which point he will be a dragon but still useless. You must pay 16 million cookies to unlock the first aura, Breath of Milk, and subsequently an amount of buildings to get more auras and an upgrade, as listed below. Sacrificing buildings reduces the cost back down to the normal cost for that amount of buildings, and switching an aura forces you to sacrifice one of your highest building. If you do not own any buildings it is free to switch an aura.

Petting
With the heavenly upgrade "How to pet your Dragon" which costs 100 billion heavenly chips, you can select Krumblor and click it to pet it; you may recieve an upgrade if it is a grown dragon, rather than hatchling or younger. Each of the four upgrades which are unlocked by petting him is randomly assigned to its own quarter of each hour, the times being XX:00-XX:14 for the first, XX:15-XX:29 for the second, XX:30-XX:44 for the third, and XX:45-XX:59 for the last. During the timeframe of an upgrade you have 5% chance of unlocking the upgrade each time you pet it, and it can simply be repeatedly clicked be unlocked.

Strategy
At the start of each ascension, get Breath of Milk and slot it. You will not need any other auras until you have 100 prisms, so you can wait until then before proceeding, or sacrifice them when it's the most cost efficient. After sacrificing the 100 prisms to unlock Radiant Appetite, switch to that as it's stronger than Breath of Milk. After that, the next useful thing is Bake dragon cookie, which requires you to first sacrifice 100 javascript consoles, so you wait until then with proceeding with sacrificing to Krumblor. You will however be sacrificing 50 of every building and only gaining +5% CpS, so make sure rebuying buildings to suitable amounts does not cost you too much. Finally, the secondary aura is immensely useful as you can slot both Breath of Milk and Radiant Appetite simultaneously, which is one of the greatest flat increase to CpS you can get from auras. In some parts of the game, Elder Battalion surpasses Breath of Milk and can therefore be switched in instead of Breath of Milk.

One hour before a sugar lump is ripe, you can switch in dragon's curve temporarily and harvest the lump. You can also do this before you go to sleep if a sugar lump would auto-harvest during the night, when you otherwise leave the game, or when you come back to the game and realise you have a ripe sugar lump. You then get the full benefit of the aura with minimal impact on cookie gains. You can also do this if you have all cookie related achievements and only want to get the sugar lump related achievements.

Before ascending, slot earth shatterer and sell expensive buildings (not necessarily the later ones, just the expensive ones) that aren't close to reaching an achievement for having X of that building. If you have chocolate egg unbought, buy it then and proceed to either buy an upgrade you will permaslot or buy buildings close enough to reach an achievement that you can do so with your amount of cookies, and afterwards sell them and redo for other buildings you can do the same with. This may give you a few more building achievements, as well as a few more heavenly chips through chocolate egg. Fierce Hoarder and/or Master of the Armory may be used in addition if it would allow you to get one more building achievement or permaslottable upgrade (highly unlikely), by swapping in the aura while you have very few of your highest building.

While hunting seasonal upgrades or garden drops while less interested in cookies, or with Cosmic beginner's luck, you can use Mind over Matter to increase the chance to get them by a little bit.

While not doing combos because you lack the mana, or while the game is progressing quite fast, you may choose to slot Dragonflight in order to have a higher chance to get a good natural clicking buff. While Dragonflight is typically bad for doing combos because the game tries to prevent Dragonflight and Click Frenzy from happening simultaneously, it is decent on its own or with a frenzy while you cannot do anything better. If you get dragonflight, switch back to CpS auras in order to get more cookies from the Dragonflight.

If you don't care about cookies or get too little cookies idly to care, and simply want to get black cat's paw, or for another reason want faster spawns, you may want to use Arcane Aura. If the reason you want faster spawns is to stack a long frenzy, you can use Epoch Manipulator as the secondary aura. In case you ever get enough buffs running to care about the cookie gain, you can always switch back to CpS auras momentarily.

While there are no buffs active, you can temporarily swap in Dragon Orbs and sell your highest building until you get a golden cookie, and repeat if it gives something else than a buff. You want to get and click the golden cookie as late as possible to get as high overlap with any buff as possible, but depending on what you are going for you usually want to click it early enough to be able to get another one in case it's not a buff.

If you have a secondary aura you can for many auras use Reality Bending together with it, to get 10% more of the aura. This can be useful for the auras Earth Shatterer, Arcane Aura, Epoch Manipulator, Fierce Hoarder, Master of the Armory, Mind Over Matter and Dragon's Curve. It does not work at all for Reaper of Fields and Dragonflight as it will not make the buffs more likely than without Reality Bending. For other auras it is practically always more useful to use other secondary auras rather than Reality Bending, or just not useful to use the aura itself.

Dragon Cursor is heavily overshadowed by Breath of Milk, as it gives at most +5% cookies and is thus never usable.

Elder Battalion usually gives around +1% CpS which is a lot less than breath of milk, other than a short time around when you get Grandmapocalypse.

Dragon God also never goes above +5% cookies, so it's never usable.

Ancestral Metamorphosis and Unholy Dominion only affects luckies, chains, and storms which means getting more CpS is simply better outside of really specific cases.

Advanced endgame strategies
Reaper of Fields can be used to add a Dragon Harvest to a combo at the simple cost of a lot of time, as a Dragon Harvest is long enough to have full overlap with a building special coming after it, and the frenzy coming before will also have full overlap as long as you either have high spawnrate and/or the frenzy stacked to a little longer than normal. Because Dragon Harvest is rare, this should only be used if you're doing large enough combos to already take a lot of time to set up. Arcane Aura can be used to speed the process up. After getting the natural cookies you want, you switch back your auras to CpS auras to get more out of the combo.

Dragonflight can also be used as a natural part of a click combo, likely as an extension to getting F+DH+BS naturally. You will need a high spawnrate, achieved by a garden of Golden Clovers, preferably mixed with Nursetulips to get an even higher spawnrate, in order to get another natural GC before the Building Special runs out. Instead of switching Dragon Harvest to a CpS aura, you will switch it to Dragonflight. If you want to reduce the chance FtHoF backfires, cast them before the natural GC spawns. Make sure to cast FtHoF before clicking the natural GC as you cannot get Click Frenzy from FtHoF while Dragonflight is active. Also click the GC you're hoping to be Dragonflight before the one you're hoping to be Click Frenzy, as Dragonflight has an 80% chance of cancelling an active Click Frenzy.

Averagely you'd gain more from clicking all Golden Cookies spawned from FtHoF, but it's quite low chance to get Building Specials from FtHoF which means you'll often not get what you want. If you want to get cookies more consistently, you can use Dragon's Fortune instead of Breath of Milk and keep a few of the GCs on-screen instead of clicking them.