Prince Hal's Strategy
It is clear in the beginning of the play that King Henry does not approve of the actions of his son, who spends most of his days in taverns with unsavory companions like Falstaff. However, the king is unaware that Hal – who addresses the audience directly to inform them – is actually hyper-aware of his future role as king, and is intentionally crafting a bad reputation for himself so that his "transformation" upon assuming the throne is more impressive. This is indeed what happens, as Henry V begins with noblemen discussing how much Hal (now King Henry V) has been changed for the better in his position as king.
King Henry Disguises
Before the battle with Percy's forces, King Henry makes the decision to send imposter soldiers into battle disguised as him in order to distract the enemy while preserving the king (in Medieval England, when the play takes place, kings fought alongside their soldiers in battle). This is an ironic decision of Henry's for two reasons: first, having so long criticized Hal for his penchant for dress-up and disguise, the king now adopts one of his son's seeming antics as military strategy. Second, the Percys have accused Henry of being an imposter to the crown (having taken it from Richard II), and now he floods his battlefield with imposters of his own.
Falstaff's Plea
Early on in the play, while Falstaff and Prince Hal are role-playing as King Henry and Hal, Falstaff pleads with the "king" (Hal in disguise) not to banish him along with Hal's other companions. The moment is ironic because it showcases Falstaff's sense of self-awareness as someone who realizes that eventually, Hal will have to cut ties with him in order to assume his kingly duty. When "Henry" does indeed banish Falstaff in their role-play, it foreshadows his rejection of his companion in 2 Henry IV.
Percy Praise of Richard
In plotting the rebel attack of the Percy family, Hotspur and others attempt to portray King Henry IV as an imposter who stole the crown from Richard II. In so doing, they often romanticize Richard – Hotspur refers to him as a "sweet rose" – while demonizing Henry as a threat to English prosperity. In reality, however, the Percy family was instrumental in aiding Henry's pursuit of the throne; they contributed to deposing Richard II and were complicit in the very plot they now criticize.
