Tash in "Dragon Age: Shadowkeep" is a unique teammate in the game. If you want to quickly increase Tash's favorability, you can choose to prefer sarcastic or aggressive responses in these tasks. Although they Not averse to friendly responses. They will also favor a fearful response if the question specifically involves the undead and witchcraft.
How to quickly increase Tash’s favorability in Dragon Age Shadow Guardian
You don't complete these quests or events together to instantly unlock the next one - you need to maintain a high enough relationship, and certain important quests are locked to specific parts of the game. With the former, there are a few things to keep in mind. The most obvious is taking Tash with you on a number of missions - completing each mission will give you a slight opinion boost with the companions you're traveling with.
In these tasks, Tash prefers sarcastic or aggressive responses, although they are not averse to friendly responses. They will also favor a fearful response if the question specifically involves the undead and sorcery, but be aware that Emirich may dislike these responses and will often default to participating in these quests.
In the Siege of Westhope, you must choose whether to knock down or persuade the first guard, with all seven companions reacting violently. Tash is very much in favor of you taking him down, as are Hardin, Neve, Lucanis, and Davlin, so it's a wise choice overall. This is the only 50/50 decision that has a significant impact on Tash's favorability.
Despite his distaste for all undead, Tash's closest companion at the lighthouse is Emirich. When you see them arguing in Emirich's office, you can intervene. Here, you should either side with Tash in thinking the undead are scary (which in turn will lower Emirich's favorability), or sit on the sidelines and say they're more similar than they realize, which won't improve either person The goodwill will not be reduced.
Whether you encourage them to change the subject or find common ground, it won't affect the relationship, but it will change future conversations between the two.
