What are some Pathfinder IKEA Tarrasques?

[Coidzor]

The Emerald Legion (http://www.giantitp.com/forums/showthread.php?101587-D-amp-D-3-5-The-Emerald-Legion-Mass-Producing-Ikea-Tarrasques), for example, even with Voidmind and Illithids ported over, would no longer work due to the lack of RHD from becoming a Lycanthrope.

I know that one can make Trompe L'oeil construct versions of Waxwork Constructs or Adamantine Golems to get something that's immune to HP damage outside of specific situations or types of damage, and then even if it does get destroyed, it essentially has a phylactery that reforms it, but I'm certain that there's a way to improve upon this or make it even better.

[unseenmage]

Well, the 'Constructs Are Magic Items' rules interpretation would allow you to literally add magic items to your monster.
It's got more anecdotal evidence backing it in 3.x but the core conceit, that Craft Construct is an Item Creation feat and thus Constructs must be Magic Items, remains true in PF to my knowledge.

Mass producing Simulacrums of theoretical monsters can be even easier than using Trompe L'oeil. Especially so if Trompe L'oeil or Alter Ego are used as the basis for the Simulacrum. Just make sure the monster superpowers you're after aren't affected by being Simulacrum-ized.

PF actually has a monster building system with rules for copy-paste-ing monster abilities from one creature to another. The calculations to adjust a custom monster's CR are a pain but work pretty well.
It's worth noting that the custom race building rules effectively can act as another source of custom monsters in a pinch.

Templates are always a golden standard. I am especially fond of the Amalgam template from Green Ronin's Advanced Bestiary.
The Advanced Simple Template wound up banned at our table, and we were playing Mythic, Technology Guide, monster character shenanigans.
If you're just looking for an obscenely powerful creature the Advanced Simple Template will do the job.

My apologies that the above is mostly just guidelines.
For more specific instructions the best I can offer is the Clockwork Spacewhales thread linked in my sig. Though most of its content predates my learning about Trompe L'oeils and Alter Egos.

[Florian]

but I'm certain that there's a way to improve upon this or make it even better.

There is, but it´s a two man con to pull of and a pretty high-level tactic (Could be done single-handedly with a gestalt build, tho, or burning WBL).

Take a look at the Nexian Channeler Medium archetype and the Personal Spire feature when channeling Nex. You can summon copies of whatever you have stored in your personal demiplane when channeling Nex.

Now a focused Illusionist can make a simulacrum of about everything, from nascent demon lords to great old ones when pushing CL high enough.

Now combine those two. Create the simulacrum, store it in the personal demiplane and spam it.

[sinceresarcasm]

Half Balor moss troll with the mutant template for mind affecting immunity could also be a good start.