Alt click on a node connection automatically disconnect it from the other nodes. And there is some nodes which can be easily summoned by pressing a key and clicking at the same time. Like B+click will place a branch, and S+click a sequence.
If you're willing to compile it, Aseprite is a great option as well.
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Here is another outstanding 2016 GDC talk for you to check out. An independent designer Robin-Yann Storm, a developer who has worked on the latest Hitman, explains both the good and bad sides of many different engines and editors, from a level designer point of view, and how tool creators can help level designers achieve their vision through streamlined design.
This talk focuses on five different editors: Unreal, Hammer, Unity, The Creation Kit and 3ds Max. The developer shows how they can improve from a UX & UI point of view.
The developer states that the most important thing is to keep everything in the zone. You must come up with a design won’t lead your players to boredom and this challenge might be quite tricky.
Essentially, this a must-watch talk for all level designers. What is more, it can help you choose the right engine without trying everything for yourself.
Make sure to check out the developer’s website that is full of useful content for tool and level designers.