Uncle Kitty's Guide to Template Based Shenanigans

[bhu]

So You've Decided to Become A Giant (wip)

You're kind of limited if you want to become a Giant.  Half-Troll/Scrag will work if you're an Animal, Dragon, Fey, Humanoid, Magical Beast, Monstrous Humanoid or Outsider.  Appropriately sized Constructs can take Incarnate Construct.  If you use unofficial stuff Animals and Vermin also get Beasthead Giant.  Aberrations, Elementals, Oozes and Plants must first use Templates to become Fey, Dragon or Outsiders to access Half-Troll.     Undead and Deathless must first become Outsiders.

Spells Targeting Giants
Antilife Shell
Bane Bow
Bladebane
Detect Favored Enemy
Foebane
Last Judgement
Nature's Wrath
Return to Nature
Slaying Arrow

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So You've Decided to Become A Humanoid (wip)

Unless you're willing to jump through some hoops, were back into Wish or homebrew territory here.  The only Template allowing you to become Humanoid is Incarnate Construct, which means you must be a Construct in Humanoid form, and Medium or smaller.  That pretty well leaves out Animals, Magical Beasts, Oozes, Plants and Vermin as well as many Aberrations, Dragons, Elementals, Fey, Giants, Monstrous Humanoids and Outsiders.  Most of the Templates changing you to Construct will make you Mindless or hamper your mental faculties, while Incarnate Construct will strip you of most of your Abilities.  Most people probably won't see any point to that kind of sacrifice.   Most Undead/Deathless will be humanoid enough in form, but there's few options for them becoming a Construct.

Spells Targeting Humanoids
Antilife Shell
Bane Bow
Beckon Person
Bladebane
Charm Person
Create Chosen One (humans only)
Curse of Lyacanthropy
Daze
Detect Favored Enemy
Dominate Person
Enlarge Person
Foebane
Greater Enlarge Person
Greater Reduce Person
Greater Seed of Undeath
Hold Person
Last Judgement
Mass Enlarge Person
Mass Reduce Person
Nar Fiendbond
Nature's Wrath
Reduce Person
Return to Nature
Seed of Undeath
Slaying Arrow
Snake Barrier
Spider Curse
Stay the Hand
Steal Life
Steal Size
Were-Doom

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So You've Decided to Become A Magical Beast (wip)

Only Animals and Vermin have Templates allowing them to become Magical Beasts.  Since your options for becoming an Animal or Vermin are limited to Wish or Homebrew (or a Feat in the case of Animal), your options for being a Magical Beast are likewise problematic.

Spells Targeting Magical Beasts
Antilife Shell
Bane Bow
Bladebane
Detect Favored Enemy
Foebane
Nature's Wrath
Return to Nature
Slaying Arrow
Snake Barrier

[bhu]

So You've Decided to Become A Monstrous Humanoid (wip)

Becoming a Monstrous Humanoid is tough unless you're a Humanoid.  Animals can do it via Anthopomorphic Animal, and Ogres have Ogre Titan.  Magical Beasts and Vermin can also take Tauric Creature.  For any other Type, you will have to become Humanoid first, and as previously mentioned that will be a bit of a bitch.

Spells Targeting Monstrous Humanoids
Antilife Shell
Bane Bow
Bladebane
Detect Favored Enemy
Foebane
Last Judgement
Nature's Wrath
Return to Nature
Slaying Arrow
Snake Barrier

[bhu]

So You've Decided to Become An Ooze (wip)

Once again you're pretty much back to Homebrew material or Wish pending DM approval.  Only two templates allow you to become an Ooze (neither of them truly suitable for PC's): Living Spell for spell effects, and Skitterhaunt for Vermin.

Spells Targeting Oozes
Antilife Shell
Bane Bow
Bladebane
Dawn Shroud
Dehydrate
Detect Favored Enemy
Flaying Tendrils
Foebane
Ooze Puppet
Slaying Arrow
Sunbolt

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So You've Decided to Become An Outsider (wip)

Most Types have a pretty decent spread of Templates allowing them to become an Outsider.  Only Undead and Deathless are truly limited in their options, and only non-living Constructs will have to change Types.

Spells Targeting Outsiders
Bane Bow
Bladebane
Demon Dirge
Denounce
Detect Favored Enemy
Devil's Blight
Exorcism
Foebane
Holy Storm
Light of Mercuria
Light of Venya
Nature's Wrath
Nether Trail
Orders Wrath
Profane Item
Return to Nature
Revive Outsider
Righteous Exile
Sacred Item
Slaying Arrow

[bhu]

So You've Decided to Become A Plant (wip)

Options for becoming a Plant are somewhat limited.  Aberrations only have Wood Element Creature unless they use another Template to change Type first.  Fey, Humanoids, Vermin and Giants are likewise limited to Greenbound Creature unless they change Type.   Animals are the most versatile with three Templates they can use.  Constructs must become Aberrations (Corrupted/Corrupted by the Abyss/Worm That Walks) or Giants/ Humanoids (Incarnate Construct) or Fey (Living Constructs only).  Dragons have a few templates that will allow them to become Fey, Giants or Aberrations so they can access a Template hat will turn them into Plants.   Elementals and Oozes have a few options to become Aberrations, Dragons or Fey before turning Plant.  Magical Beasts, Outsiders and Monstrous Humanoids must first become an Aberration, Dragon, Fey or Giant.  Undead and Deathless only have a few Templates that will turn them into Aberrations if they wish to become Plants. Subjects can become Plants temporarily via Arboreal Transformation.

Spells Targeting Plants
Antilife Shell
Antiplant Shell
Awaken
Bane Bow
Bladebane
Blight
Command Plants
Control Plants
Deadly Sunstroke
Dehydrate
Desiccate
Despoil
Detect Animals or Plants
Detect Favored Enemy
Diminish Plants
Evergreen
Flaying Tendrils
Foebane
Forest Eyes
Forest Voice
Junglerazer
Mass Awaken
Mass Desiccate
Profane Item
Slaying Arrow
Speak with Plants
Sunbolt
Wood Rot
Wooden Blight
Zone of Natural Purity

[bhu]

So You've Decided to Become An Undead (wip)

Except for certain types becoming an Undead really isn't all that hard.  Non-living Constructs will possibly have to change Type, but everyone else has plenty of options.  On the downside, lots of spells now target you

Spells Targeting Undead
Abolish Shadows (Shadows and similar beings only)
Anger of the Noonday Sun
Aura of the Sun
Bane Bow
Bladebane
Bleakness
Bone Chill
Command Undead
Consecrate
Consecrate Battlefield
Control Undead
Cure Critical Wounds
Cure Light Wounds
Cure Minor Wounds
Cure Moderate Wounds
Cure Serious Wounds
Darts of Life
Dawn Burst
Dawn Shroud
Deadly Sunstroke
Defile Snow and Ice
Deific Vengeance
Desecrate
Desecrate Battlefield
Detect Favored Enemy
Devastate Undead
Disguise Undead
Disrupt Undead
Disrupting Weapon
Dread Blast
Dust to Dust
Estanna's Stew
Expose the Dead
Eye's of the Zombie
Flaying Tendrils
Foebane
General of Undeath
Grave Strike
Greater Disrupt Undead
Greater Harm
Hallow
Harm
Halt Undead
Haunt Shift
Heal
Healing Spirit
Hide from Undead
Holy Fire
Inflict Critical Wounds
Inflict Light Wounds
Inflict Minor Wounds
Inflict Moderate Wounds
Inflict Serious Wounds
Invisibility to Undead
Leech Undeath
Life Bolt
Light of Courage
Light of Faith
Light of Mercuria
Light of Purity
Light of Venya
Light of Wisdom
Manifest Death
Manifest Life
Mass Cure Critical Wounds
Mass Cure Light Wounds
Mass Cure Moderate Wounds
Mass Cure Serious Wounds
Mass Inflict Critical Wounds
Mass Inflict Light Wounds
Mass Inflict  Moderate Wounds
Mass Inflict Serious Wounds
Mass Harm
Mass Heal
Moon Blade
Moon Bolt
Nature's Purity
Nature's Wrath
Negative Energy Aura
Negative Energy Wave
Night's Caress
Panacea
Positive Energy Aura
Positive Energy Protection
Proper State
Radiance
Rebuking Breath
Rejuvenating Light
Rejuvenative Corpse
Retributive Enervation
Revive Undead
Sacred Item
Searing Light
Seek Eternal Unrest
Semblance of Life
Shadow of the Dark Queen
Shroud of Undeath
Slaying Arrow
Soldiers of Sanctity
Spark of Life
Stone Bones
Sun Bolt
Sunbeam
Sunburst
Sunrise
Undead Bane Weapon
Undead Eyes
Undead Lieutenant
Undead Mask
Undead Torch
Undeath's Eternal Foe
Undying Aura
Unhallow
Unliving Weapon
Vile Death

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So You've Decided to Become A Vermin (wip)

Much like Animal there are no templates in this list, third party or otherwise that allow you to become a Vermin.  So once again you're left with homebrew or Wish.  Assuming there's a reason you would actually want to.  If the DM insists you become Mindless, you can't be a PC.  But without the immunity to Mind-Affecting affects that Mindless brings there's not much reason to become a Vermin.

Spells Targeting Vermin
Antilife Shell
Armored Vermin
Bane Bow
Bladebane
Detect Favored Enemy
Dominate Vermin
Foebane
Giant Vermin
Junglerazer
Repel Vermin
Slaying Arrow

[bhu]

So You've Decided to Become A Deathless (wip)

The Sacred Watcher Template is your only option for becoming a Deathless, and to take it you must be Good and one of the following Types: Aberration, Animal, Dragon, Giant, Humanoid, Magical Beast, Monstrous Humanoid, or Plant.  Constructs must first become a Humanoid or Giant via Incarnate Construct.  Elementals must become an Aberration (and then find a way to become good because any Template giving them Aberration gives them the wrong Alignment), or a Dragon (Half-Dragon or Drake, must have Good Alignment).  For Fey becoming a  Plant via Greenbound Creature or a Dragon of the appropriate alignment via Half Dragon is best.  They could also become an Aberration or Giant via Templates but would then need to find a way to alter their inappropriate Alignments.  Oozes have no options besides becoming an Aberration (and finding some way to change Alignment after) or a good-aligned Half-Dragon.  Outsiders can become Giants (Half-Troll, will still need to switch Alignment), Dragons (appropriate Half-Dragon/Drake types), or Fey via Folkloric Fey/Half-Fey/Unseelie Fey before becoming something else (and probably still need to change alignment).  Vermin actually have a plethora of options for becoming some other Type (usually Magical Beast) before taking Deathless.  Undead have almost no options.  They must first take a Template to become an Aberration and then find a way to change Alignment, or take one of the few options allowing them to become a Construct, before taking Incarnate Construct, and then taking Sacred Watcher assuming they can become Good.

Spells Targeting Deathless
Bane Bow
Bladebane
Consecrate
Consecrate Battlefield
Control Deathless
Deathwatch
Desecrate
Desecrate Battlefield
Detect Favored Enemy
Detect Undead
Disrupt Undead
Foebane
Hallow
Halt Deathless
Searing Light
Slaying Arrow
Undying Aura
Unhallow

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Spells That Grant Templates

Axiomatic Creature (Axiomatic) Book of Exalted Deeds
Conjure Ice Beast I-IX (Ice Beast) Frost burn
Create Frenzy Dog (Frenzy Dog) web enhancement
Curse of Lycanthropy (Lycanthropy) Complete Divine/Spell Compendium
Demonic Blood Infusion (Fiendish) Ghostwalk
Ghost Companion (Ghost) Ghostwalk
Greater Spider Form (Fiendish) Drow of the Underdark
Holy Mount (Celestial) Spell Compendium
Iconic Manifestation (Anarchic, Axiomatic, Celestial or Fiendish) Complete Champion
Incarnate Construct (Incarnate Construct) Savage Species
Lesser Spider Form (Fiendish) Drow of the Underdark
Mineralize Warrior (Mineral Warrior) Underdark
Nar Fiendbond (Half-Fiend) Lost Empires of Faerun
Sanctify the Wicked (Snactified Creature) Book of Exalted Deeds
Spider Form (Fiendish) Drow of the Underdark
Summon Desert Ally I-VIII (Dustform) Sandstorm
Undeath After Death (Crypt Spawn) Magic of Faerun
Vile Death (Fiendish) Savage Species
Were-Doom (Lycanthrope) Book of Vile Darkness

Spells That Detect Inherited Templates
Discern Bloodline (Races of Destiny)