Maintenance for the week of April 20:
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• [COMPLETE] EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
Your question is pretty broad however, use them offensively to set up a full burst combo and confirm a kill, or use them to escape in a sticky situation. They pair well with cast time abilities, for example dark exchange on sorcerer.
Elswyer did introduce some new alchemy ingredients but I don't think any of them works with immovable. I still use the mag+health+immovable pots. Detect+mag+immovable if I come across a cloak spammer.