This could be a change to the medic/support class I mentioned earlier, but I think this skill would generally be good in any case.
For phoenix-type skills, You set up a 'portal' type thing just like the strider ultimate (using +ability I guess), and when the respawn activates you/your teammates respawn at the portal location, instead of in the same location/back at spawn/on you (as I suggested with the medic class). If no portal is set you respawn at your starting location by default. This can be used to set up 'reinforcement' points behind the front line in your team, be placed at a bombsite or whatever.
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As a separate class:
Alchemist:
Alchemist restricted to knife/grenades only. 6 skills/5 levels
Potion Set: As levels increase, you get more grenades at spawn (like hell hunter, but flash/smoke/nades all at once instead of on separate skills).
Potion of Health: Smoke grenades heal teammates/self (5hp/second at max for however long smoke nades last)
Deadly poison: Upon dealing damage with a knife, enemies are drastically slowed (-80% movement speed at max) and take damage over time (5 hp/sec for 5 seconds at max)
Potion of Clarity: Upon dealing damage with grenades, cloak effects are removed, and enemies glow for longer periods of time (10 seconds at max)
Debilitating poison: Flashbangs, as well as blinding, inflict banish/drug for longer periods of time. (No idea how this could be coded, since teammates are also affected by your flashbangs)
ULTIMATE: Potion of invigoration: Sacrifice half your current health for greatly increased speed, knife damage, and lower gravity for a short time. (+100% speed/knife dmg, -50% grav for 8 seconds at max) Has a fairly long cooldown.
I feel like that could be really cool, although I'm not sure on the potion of health, it could either be OP, or in any case doesn't really fit with the rest of the skills aside from the ultimate (blinding opponents, hitting ulti, running in and killing people in the room before retreating to heal with the smoke nades sounds cool in my head). Perhaps instead smoke appears for your enemies but there is not smoke for yourself, as if you had no smoke hacks? Would make for some nice strategic moments as you plan your assault down the hallway with the ultimate. If this were to happen though, then the sacrificing of health for the ultimate would be removed. Also the potion of clarity, it just feels like the skill to go with nades should be damage based, but I like the idea of removing cloak and glowing opponents. It hopefully wouldn't be TOO hard on vagas since hell, it's a grenade and we have limited amounts of them, and the followup damage can only come from a knife (or teammates). I have no idea how this stuff could be coded, especially the flashbangs, but if hell hunter could be coded perhaps this could.