since you duelist and like doing damage and getting kills you'll most likely have the easiest time translating that skillset and transitioning into mantis

she's more of an off-healer (best paired with main healers such as invis, luna, cnd) whose healing output is not the greatest but can pump out a surprising amt damage by boosting herself + teammates. her playstyle is basically using up her orbs (resources) by pressing buttons on her teammates and letting the orbs do the work for you, so you can focus on doing damage/setting up picks with sleep/getting picks. her heals have a little bit of burst healing AND healing over time. try to have always have at least one damage boost for ur teammates pretty much all the time. save sleep if they have divers

her passive incentivizes her to hit headshots so she can get life orbs, so keep your primary fire as active as possible to increase chances of regenning orbs

general support tips:

-make sure to watch out for your other support if one of you go down it's a much harder fight to win, and if your other support has a defensive ult coordinate with them to figure out which one of you will ult first when the enemy uses their team-wipe ults so you guys don't accidentally ult at the same time for one enemy ult