And of course, farming bosses using giant hunter as soon as possible is pretty much a requirement if you want to survive 10+ challenge ranks where you really need that gear as soon as possible to tip the scales back in your favor.
Never done that particular strategy, and done plenty of 20+ challenge ranks so I think there's more variety available for you to discover.
The new creature, eleoxotl, is a lightning support that is weak, but can give actions to allies damaged by electric damage, including volt sword passive effect, though they have to take health damage, so if they get shields via passive abilities and so on, that means no bonus, though its rarity makes it hard to get one that is high enough level to stick around, though their lack of growth on durability or offense makes it a moot point. Still, if you combine it with a unique shadow character that has insulated trait which reduced lightning damage by 75%, and has abilities that damage everyone that is on water, suddenly you have a character combo that will kill anyone within range as long they have mana to spare and water to spread around.
Elexolotl has a special feature where it has a vastly increased chance to appear on day 0. Insulated actually replaces your defensive (aka egg) type's lightning damage modifier with a hard coded 0.5. I suppose for a water type that would look like a 75% reduction, but there are units that won't see any benefit at all. This differs from the Heat Resistant genetic trait, which multiplies your existing fire damage modifier by a further 0.5. Lightning damage also does double damage to anyone on a water tile. As for the volt blade's passive, it scales with mg so if you do luck into an Elexolotl you can tank your mg stat with traits and basically get infinite regular attacks.
you can literally upgrade your way to max gene characters early on
If that's all you want, 4th MC characters can start with max genetics using evolved and HiddenPower. With the hatcher perk as well, you can literally hatch characters with max genetics on day 0. If you use one of the two guardians (Veila/Alt. Avy), you can even absorb a ton of amazing genetic traits from your starters using soul drain or even the (usually awful) bloodline trait to ensure full 10s.
For shapeshifter, it allows you to change element types for attack/defense, which also affects egg results, but you cannot put crystal/true ones, let alone back, so if a character that has crystal type/true damage as a base gets changed, well, no more getting it back unless you fuse/breed it. Elemental lock modifier makes it really useful to have in order to mitigate its disadvantage though, in normal games it takes plenty of points that better be spent on improving yourself.
Evo's type shifting is way better than you're giving credit for here. Just being able to switch attack types to something like lightning is amazing -- water terraforming is abundant and cheap, especially with item upgrading giving extra uses and range to the water hammer.
For defensive types, it enables a large amount of truly broken synergy. There's a lot of abilities and bonuses that check egg (defensive) type. For example, the Bee Queen's onCombatStart passive gives all Floral units on your team 5 magic charges. Bee Queens have a normal type, but you can change them to Floral and then fill an entire team with them to give them all 20-30 magic charges (x2-3 magic).
For creator, it gives a skill that summons 6 tentacles, which is good, but only if you can get that much slime tiles, meaning in cases where you cannot have slime as soon as possible like the unknown character, it is not really that great of a skill, especially if your strategy doesn't involve slime characters, which is very likely considering the changing nature of the gameplay.
This one can be tricky to use, but it's extremely strong when set up well. Two tips: 1) Creation gets a special consumable in her crafting menu called the slime bomb. It's a 0 AP (free action) that creates slime in combat (and some other useful things like slowing an enemy or summoning a tentacle).
2) You can terraform tiles on the OW into slime pretty easily. This makes the entire battlefield start out completely covered. Any unit with inherit SlimeTrail onMove passive has an OWSkill that can terraform even tiles enemies are standing on into slime (placing a Hive will also do this, but Hives don't change water or a few other special tile types).