Found one of them, thanks to the search engine. The one with the slayer army arriving in a mist and Buffy wearing a cloak is Sapphire Haze
by lilladybug. (On EF too).
Summary: In response to challenge #329 on the Bloodshedverse, from Marika.
«It's the last episode of angel and Angel, Spike, Gunn, and Illyria are the last remaining fighters. As they plunge into battle, Buffy suddenly comes in with an army of slayers. Buffy still doesn't know that Spike's alive.
Still looking for the one where Spike dusts saving Buffy and rematerialises as a human being...