Here is my updated guide [April 16, 2010]. Credits go out to Pet Professor’s thread [here] and Ruichi’s thread [here]. I wanted to skim over what they’ve said and show you what they’re talking about.

Following what was mentioned in the other guides, you want your final pet to have nice fusion bonuses which include [affinity that corresponds to your own skills], Accuracy, and Resilience. This makes for the "ideal" fusion pet because it decreases the amount of misses you’ll make and increase the amount of times an enemy will miss you.

Now here is my view on creating the [Ultimate Fusion Pet].

Step 1: Obtain your [Fusion Pet]. For my example, we are going to be using an Pyra/Fierce Cloudwisk Captain [Fusion Bonuses: Unda/Accuracy/Resilience].

Step 2: Collect and raise 10 sheep to lv30. Make sure your main sheep is the same affinity as your fusion pet. In this example, use an Pyra/Fierce sheep. The other 9 sheep can be any affinity. (It does not matter what they are.) The process should look something like this.

[Main-Sheep] + [Sheep#2] = [Sheep-Meld1]
[Sheep-Meld1] + [Sheep#3] = [Sheep-Meld2]
[Sheep-Meld2] + [Sheep#4] = [Sheep-Meld3]
[Sheep-Meld3] + [Sheep#5] = [Sheep-Meld4]
[Sheep-Meld4] + [Sheep#6] = [Sheep-Meld5]
[Sheep-Meld5] + [Sheep#7] = [Sheep-Meld6]
[Sheep-Meld6] + [Sheep#8] = [Sheep-Meld7]
[Sheep-Meld7] + [Sheep#9] = [Sheep-Meld8]
[Sheep-Meld8] + [Sheep#10] = [Sheep-Meld9]

*Note: Mutation will occur between melds 3~9 — that’s a good thing. The reason is, whatever the sheep mutates into will have a greater MAX HP growth rate than the sheep.

Step 3: Collect and raise 7~10 beastkin pets with the same affinity as your fusion pet to lv30. In this example, each pet will be Pyra/Fierce. In this process, you are now creating a secondary pet (a sacrificial pet, or support pet). For this example, I will be using a Storm Raiders — which have commonly have a 35+ HP Growth Rate. Pick the Storm Raider with the highest HP growth rate (36.00~37.50) and use this as your [Main-Storm Raider]. Meld it with more Storm Raiders until you reach at least 45HP Growth. The more HP the better, but more than 50HP for this step is unnecessary.

[Main-Storm Raider] + [Storm Raider-#2] = [Storm Raider--Meld1]
[Storm Raider-Meld1] + [Storm Raider-#3] = [Storm Raider-Meld2]
[Storm Raider-Meld2] + [Storm Raider-#4] = [Storm Raider-Meld3]
[Storm Raider-Meld3] + [Storm Raider-#5] = [Storm Raider-Meld4]
[Storm Raider-Meld4] + [Storm Raider-#6] = [Storm Raider-Meld5]
[Storm Raider-Meld5] + [Storm Raider-#7] = [Storm Raider-Meld6]
[Storm Raider-Meld6] + [Storm Raider-#8] = [Storm Raider-Meld7]
[Storm Raider-Meld7] + [Storm Raider-#9] = [Storm Raider-Meld8]
[Storm Raider-Meld8] + [Storm Raider-#10] = [Storm Raider-Meld9]
[Storm Raider-Meld9] + [Storm Raider-#11] = [45HP-Storm Raider]

*Note: If the two pets you are melding have the same or very similar growth rates [35.02 + 35.05] you will not see much of an increase. Please avoid these melds by picking another pet to meld with.

*Note: Certain pets do not mutate when melding; for this step whether the pet mutates or not does not make a difference.

Step 4: Level both your [Sheep-Meld9] and your [45HP-Storm Raider] (ideally to lv90) as best you can before melding them. You can meld them at whatever level you see fit, but for this step, the higher the level, the better the results — the growth that will transfer from your [45HP-Storm Raider] to your [Sheep-Meld9]. After you’ve melded these, you should receive a [Sheep-Meld10] (unable to say which one it will be due to mutation) with 70~95HP Growth Rate. Again, the higher the level, the better the growth rate — some people meld when both pets are lv80; I prefer to meld when both pets are lv90.

[Sheep-Meld9] + [45HP-Storm Raider] = [Sheep-Meld10] aka [Super-Mutated-70~95HP-Sheep]

Final Step: Meld together your [Fusion Pet] with the [Super-Mutated-70~95HP-Sheep]. Again, and more importantly at this stage, please be sure your pets are around lv90 before you meld — or high enough that the preview of your fusion pet shows it will max the HP.

[Fusion Pet] + [Super-Mutated-70~95HP-Sheep] =
[Fusion Pet-Meld1] aka [Ultimate Fusion Pet]

With this, your new [Ultimate Fusion Pet] will have maxed HP. The maxed stats will appear in orange highlight.

Thank you for reading and I hope I may have cleared up a few questions many of you may have!

Please remember this process is not for everyone! By no means must you be able to do this in order to level, or compete with most players in the game. Also note that the stats I used in this example are not set in stone! — this is merely a guideline for how a typical process would be structured. Using different pets, obtaining different pre-meld HP, or reaching different levels will make results vary. Please use this as a guideline and do what works for you!

Credits go to s0jukill’s.