Brisela, Voice of Nightmares is made when Gisela, the Broken Blade and Bruna, the Fading Light are just on the battlefield together, while Hanweir, the Writhing Township is made through an activated ability that melds Hanweir Battlements and Hanweir Garrison together
In MTG, ramp refers to anything that helps you generate more mana on future turns
" Tarkir: Dragonstorm Mechanics"
If that creature has toxic, instead it gets +2/+2 until end of turn
Also, this aura offers a huge buff to a creature, if you're interested in the mechanics, of course, and not just in how very cool the artwork is
Notably, Korvold will benefit from any Magic card type being sacrificed, not just Treasures, so the deck can also use sacrifice-related cards like Sakura-Tribe Elder