The Ember Swarm: the arena and the altar's bargain

The Effigy Altar's floor is its arena now — the doors seal, the stairs lock, and between waves the altar offers boons and curses that stack into a richer hoard.

Some floors hold an Effigy Altar in their biggest room — the Swarm's arena. Touch it and the doors slam shut, the stairs seal and the waves pour inside. There is no leaving until the Swarm ends: hold wave 20, or bank the hoard at a checkpoint and walk.

Touch the Effigy Altar in its arena and the doors seal: hold the waves, take an effigy every minute, or bank the hoard and go
Waves	Checkpoints (the way out)	Live foes at once	Effigy pick	Swarm Sapper
20: +2 foes each wave, +2 per extra hero	after waves 5, 10, 15 the golden Effigy of the Hoard joins the next pick	22	one about every 60s; solo play waits, co-op gives 10s	each wave; 7s after its last foe to fell it, or the next wave is Empowered

The floor's largest far room is the Swarm's arena: touch its Effigy Altar and the doors slam shut and the stairs seal until the Swarm ends. Up to 20 waves pour in, and sellswords and pets fight uncapped here, the only place the game lets crowds loose. About every 60 seconds the altar offers three effigies and you take one; each is a boon that stacks up to five ranks, 12 in all. Every wave brings a Swarm Sapper that only your own hits can hurt; if it lives past the wave's end the next wave comes Empowered. The hoard pays for the waves held and the picks taken, and the best Swarm of the week tops the weekly board.

The picks are the point: since 0.27 the altar offers three effigies about every minute, each a boon that stacks, and the hoard pays for the waves you hold and the picks you take. Press on past a checkpoint for a fatter hoard, or take the golden effigy and go.

Effigy	Kind	What it does	Rank 1	Top rank
Wide Flame	area	Your area skills reach wider.	Area skills +15% wider	Area skills +75% wider
Twin Bolts	projectile	Your projectile skills loose more shots.	+1 shot a volley	+3 shots a volley
Arc Thread	chain	Your hits arc on to the nearest foes.	Hits arc to 1 more foe for 36%	Hits arc to 3 more foes for 60%
Ember Burst	nova	A foe you fell bursts into flame.	Felled foes burst for 47% of their health in 2.3 tiles	Felled foes burst for 95% of their health in 3.3 tiles
Whetstone	stat	The whole party hits harder.	+10% damage	+50% damage
Quickening	stat	The whole party strikes and moves faster.	+8% attack speed, +4% move speed	+40% attack speed, +20% move speed
Ironhide	stat	The whole party is tougher.	+6% health, 2 damage reduction	+30% health, 10 damage reduction
Bloodletting	sustain	A foe you fell mends you.	Heal 0.6% of your health a kill	Heal 3.0% of your health a kill
Cinder Halo	aura	Flame circles you and scorches what presses close.	Burns foes within 2.2 tiles every half second	Burns foes within 3.0 tiles every half second
Stormcall	aura	Lightning falls on a foe near you every few seconds.	A strike every 6s on 1 foes	A strike every 2s on 3 foes
Ember Ward	sustain	A ward of banked fire renews itself around the party.	A ward of 4% health every 8s	A ward of 20% health every 8s
Fortune	reward	Luck and the altar's hoard grow.	+20% gold, +8% magic find, 1 extra hoard share	+100% gold, +40% magic find, 5 extra hoard shares
Effigy of the Hoard	way out	The altar yields: take the hoard and end the Swarm.	Ends the Swarm and pays the hoard	ends the Swarm and pays the hoard