The Second Upgrade!

[Ryli]

Colossal Dragon - Massive Dragon - There's no room for any more creatures
Plague - Improved Plague - Black Plague
Devonian Dragon - Silurian Dragon - Retired Dragon - Bone Dragon - Dust
Procrastination - Turtle Shield - I'll name this one later
Momentum - Unstoppable - The opponent's about 200 miles back
Short Bow - Long Bow - Sniper Rifle
Heal - Improved Heal - Shard of Divinity
Deflagration - Explosion - Nuclear Bomb

[RRQJ]

Procrastination - Procrastination - I'll name this one later

i c wut u did thar

[RRQJ]

lawl, I actually didn't notice that.

[Hyroen]

Discord -> Discord -> Dislike

[n00b]

Ehem, I believe I speak for all of us when I say this

Artic Squid -> Artic Octopus -> Artic Fail

Flood -> Inundation -> Apocalypse

Acceleration -> Overdrive -> Overpowered

I know I know, I have amazing ideas

[Sh00pdaWoop]

Armagio -> Elite Armagio -> Armedilgo.

[dragonsdemesne]

Dagger -> Dirk -> Short Sword
Quantum Pillar -> Quantum Tower -> Quantum Mechanic (hi nethack)
Schrodinger's Cat -> Schrodinger's Cat -> Schrodinger's Cat
Schrodinger's Cat -> Schrodinger's Cat -> Skeleton
Boneyard -> Graveyard -> Backyard
Catapult -> Trebuchet -> Nuclear Silo
Chrysaora -> Physalia -> Wtfhowdoispellthisulkgsoihgoaweroeurgawopriupoewarugeragalia
Holy Light -> Holy Flash -> Holy Crap
Vampire Stiletto -> Vampire Dagger -> Vampire Dirk
Drain Life -> Siphon Life -> Get a Life
Lobotomizer -> Electrocutor -> Castrator

[Rainbowninja]

Ash->Ash->Ash Ketchum

[Xenocidius]

A possible super-upgraded border gradient:

[Bloodshadow]

No one thought of this yet?

Twilight New Moon Nightfall -> Eclipse -> Breaking Dawn

[Pineapple]

Holy Light - Holy Flash - Flashing Priest
Arctic Squid - Arctic Octopus - Ant Arctic
Phoenix - Minor Phoenix - Antagon

[RavingRabbid]

Flooding -> Inundation -> Still meh.