The Grand Warden is a single-target unit unlocked at Town Hall level 11. He is the third hero in the game, being weak in physical strength and self-defense but extremely powerful in support.
Use the Grand Warden in Air Mode if you are using an air attack so he does not take damage from ground defenses (as they are not distracted by other troops) and Ground Mode when using a ground army as he will not be targeted by the Air Defenses.
Only set him to Air Mode if you are using an air attack, as, without distraction troops, he can easily be killed or otherwise heavily damaged by Air Defenses and Seeking Air Mines.
Use the Eternal Tome ability near the core so your troops can get through the core, where the most damage usually is. Against a level 5 Giga Tesla or a Giga Inferno.
He creates a buff to boost defensive troops, heroes, and the Skeletons from the Skeleton Traps.
To defend against an enemy Grand Wardens, make sure you set your Inferno Towers to multi-target.
The Grand Warden in defense mode will not be targeted by a Headhunter, due to him being considered a defensive building.