Some of these achievements are unlocked as you naturally progress through the Campaign. Some require finding hidden interactive characters/elements in many of the stages. Many are stage specific and require you meet some criteria before a Stage comes to an end while others are cumulative over all stages. The achievements list can be found in-game at the bottom left of World Map represented by a trophy icon.

Achievement	How to unlock
1,2,3...Plant!	Grow 100 barbed vines!
1.21 Gigawatts!	Cast 1210 lightning bolts.
Ace of Spades	Complete Stage 5 without building any barracks.
Beornings	Have 8 or more Runed Bears in any single stage.
Brave Little Tailor	Don't let the hero die against an Ettin on Stage 4.
Brother vs Brother	Have your Renegades defeat 50 twilight elves.
Call me Mr. Pig	Make the Razor Boars trample and kill 20 enemies.
Candy Rush	Save Hans and Ethel.
City of Splendors	Earn 3 stars on each Ancient City campaign stage.
Counter Master	Defeat 250 enemies while silenced.
D&D	Have Beresad and Ashbite defeat 100 enemies.
Ding! Ding! Ding!	Raise all 3 basic heroes to level 10.
Dogfight Ace	Have your Gryphon Riders defeat 25 Perythons.
Dwarf Falls	Save 13 barreled dwarves.
Fee-Fi-Fo-Fum!	Grow the beanstalk to the clouds!
Footloose	Perfect Parry for a total of 1000 damage.
Game of Thrones	Defeat Malicia!
Garden Song	Activate 50 magical plants.
Gargamel	Squish 10 gnomes!
Gathering the Magic	Defeat 80 enemies with the magic Blossoms.
George Fall	Find George!
Get the party started	Win stage 1 with 3 stars.
Gloomicide	Defeat 100 gloomies before they duplicate.
Gnollbuster	Defeat 900 gnolls.
Great Defender	Complete the Campaign in Normal difficulty.
Green Arrow	Defeat 500 enemies with reinforcements' projectiles.
Heavyweight Class	Stun 10 or more enemies with a single clobber.
Heroic Rush	Complete all campaign Heroic challenges.
I like to move it!	Entertain the funny lemure.
I meant the red wire	Have your soldiers avoid 50 blasting spell explosions.
I need a hero	Complete 3 stages without the hero dying.
I volunteer as tribute	Deploy 500 or more reinforcements into battle.
Iron Rush	Complete all campaign Iron challenges.
It's a kind of magic	Defeat 50 enemies with Eldritch Doom explosions.
It's a trap!	Prevent Mactans from webbing at least 8 towers.
Jurassic Lake	Crystallize a single creep for more than 10 secs.
Killer Tomatoes!	Defeat 500 enemies with the poison Vines.
Killtacular!	Crimson Sentence 10 enemies in a single wave.
Kingsfoil Leaves	Give regeneration 25 times to the same soldier.
Lullaby!	Defeat 50 sleeping enemies.
No pain, no gain	Deal over 100,000 damage with Sylvan Curses.
Not today!	Complete 7 stages without the hero dying.
Only counts as one	Defeat 10 enemies with a single thunderbolt power.
Peekaboo	Find the three playing friends.
Phantom Zoned	Keep enemies out of time for a total of 1000 seconds.
Pixiebell	Earn 3 stars on each Faery Groove campaign stage.
Rambo Style	Defeat 50 flying enemies with Arcane Burst arrows.
Red Five	Complete any stage with 5 active arcane sentinels.
Robin of Elfwood	Earn 3 stars on each Elven Woods campaign stage.
Rockstar	Earn 50 stars.
Scissorfinger	Find the matching bushes.
Shezi Banzai & Ed	End stage 3 without scaring more than 3 hyenas.
Shroom Says	Complete a 9 tap challenge of the Shroom game.
SIMCity	Build a Level 4 tower on every holder of a stage.
Sorcerer's Apprentice	Find the three apprentice relics!
Starcraft	Earn all stars from each Campaign stage.
Stardust	Earn 30 stars.
Stargazer	Earn 15 stars.
Supreme Defender	Complete the Campaign in Veteran difficulty.
Tauriel Apprentice	Make 600 Blade Dance moves.
The Art of War	Read all tip cards.
The bigger they are...	Defeat 7 Golems before they walk past half the stage.
The Bone Collector	Collect 100,000 gold from defeated enemies.
Truth or Dare	Call 13 or more early waves on any given stage.
Valar Morghulis	Mark a total of 5 targets simultaneously.
Vorpal Blade	Defeat 5 Bandersnatches only by dealing them damage.
War Never Changes	Have 1,500 of your own soldiers defeated in battle.
We are the champions	Defeat the Spider Goddess!
White Rabbit	Scare 11 idle white rabbits!
Why so serious?	Defeat Hi-Hi Enha, the Gnoll Chieftain.
Wildfire Harvest	Throw 1,000 burning nuts.
Winter is Coming	Freeze 100 enemies with the Sorcerer's Stones.