Every bolt she throws is aimed to punish you for dodging it. Kessandra reads the scattered backwash off her own missed shots and turns it straight back into the next one - so standing still and eating the hit is, perversely, the safer play.
A scripted attack roll against the target's own AC decides hit or miss - this is resolved by hand rather than left to the engine, so the mechanic can read the result directly.
Straight fire damage, nothing more. No resource changes hands.
The wasted energy scatters back into her - +1 Overcharge, capped at 5. No other boss in this bestiary is fed by its OWN misses; every prior resource here reads off what the players do.
The next round is an automatic empowered blast in a 10m radius instead of a single bolt, and the meter resets to zero.
Her epic spell answers on cue - the same illusory dragon-knight ally the real HotU spell calls, summoned to fight at her side for the rest of the encounter.
Scarlet Cave's real ceiling was Nyssara Quill at CR13; Kessandra is pitched one notch above at CR14, into 4 of the area's free Sparky slots.
She is the bestiary's first Warmage - a pure Intelligence-based battle-caster with no dedicated column, drawn from Wiz_Sorc filtered to evocation. Scarlet Cave already had a rogue/shadow prestige (Nyssara) and a pure martial hunter (Dame Thorne); Kessandra is its first dedicated blaster.
Real Epic Spell: Dragon Knight (id 638/875) - the same technique as every other epic-spell boss this round, and its capstone literally spawns the round-1 ot2_dknight blueprint rather than a new one, since that illusory knight was built for exactly this spell and has sat unused as a summon target since.