When Ertha Jo enters, create a 1/1 red Mercenary creature token with ": Target creature you control gets +1/+0 until end of turn. Activate only as a sorcery."
Whenever you activate an ability that targets a creature or player, copy that ability. You may choose new targets for the copy.
Ertha Jo turns every targeted activated ability into a two-for-one, so you build a board of cheap creatures with tap-to-target abilities (pingers, Mercenaries, equipment-style buffs) and double their value every turn. You apply pressure incrementally, then explode when you copy a big ability twice to deal lethal or stack massive buffs. The deck plays like an aggro-combo midrange shell that out-grinds opponents through doubled effects.
Doubles any targeted activated ability for free, generating huge card and tempo advantage
Built-in token on ETB and works from the command zone in a cheap color pair
Enables redundancy with pingers, Mercenaries, and tap-for-value creatures
Flexible new targets on the copy lets you split removal/buffs across multiple threats
Heavily commander-dependent; removal on Ertha Jo shuts off the engine
Many enablers are fragile 1/1s vulnerable to board wipes
Needs setup turns and a critical mass of targeted abilities to pop off
Can be slow against dedicated combo or fast aggro without interaction
Legendary Creature — Kor Advisor
: Target creature you control gets +1/+0 until end of turn. Activate only as a sorcery."