Activated abilities of creatures you control cost less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana.
: Other creatures you control get +1/+1 and gain trample and haste until end of turn.
Agatha turns every activated ability into a bargain, reducing costs by her power (minimum one mana). Pump her power with +1/+1 counters so creature abilities become absurdly cheap, then chain activations to generate mana, draw, or combo. You grind value through repeatable abilities and close with overwhelming activated-ability engines or an overrun-style alpha strike.
Massive cost reduction makes activated-ability creatures (mana dorks, untappers, pingers) extremely efficient
Scales explosively with +1/+1 counter support, snowballing into near-free abilities
Built-in anthem/overrun for a reliable creature finish
Low mana value (2) means she comes down early and starts saving mana immediately
Heavily commander-dependent; abilities cost full price without Agatha on board
Vulnerable to spot removal and board wipes that reset your counter investment
She starts at 1 power, so reductions are small until you commit resources to grow her
Counter and equipment investment can fall apart to a single removal spell
Legendary Creature — Human Warlock
less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana.