A way to balance Tahm without hurting him to bad and make it fair for his enemies
Here are some thoughts and ideas:
Passive: An Acquired Taste
Tahm Kench's basic attacks and damaging abilities apply An Acquired Taste to enemy champions, stacking up to 3 times. Against enemies with three stacks, Tahm Kench's Tongue Lash and Devour gain additional effects. After 7 seconds, An Acquired Taste stacks decay once every 0.5 seconds.
PASSIVE: Tahm Kench stores all damage he takes as Grey Health on his health bar. After taking no damage for 2.5 seconds, Tahm Kench rapidly heals for a portion of his Grey Health over time, consuming it in the process. (X Second Cooldown)
TOTAL HEALTH RESTORED: 20 / 26 / 32 / 38 / 44% of Grey Health => Now scales at level 1/6/11/16/18 (20/26/32/38/44)
Devour
Passive/Acquired Taste: Tahm Kench's basic attacks and damaging abilities apply An Acquired Taste to enemy champions, stacking up to 3 times. Against enemies with three stacks, Tahm Kench's Tongue Lash and Devour gain additional effects. After 7 seconds, An Acquired Taste stacks decay once every 0.5 seconds.
ACTIVE: Tahm Kench swallows the target enemy minion, monster, or allied champion, making them untargetable and unable to take any actions for a short duration. Devour cannot be activated for 4 seconds after using Abyssal Voyage. When a target has 3 stacks of Acquired Taste, they can be swallowed for half the duration.
What's New Swallowing enemy champions slows Tahm Kench by 95% and removes all An Acquired Taste stacks from them _and are immune to Acquired Taste for X seconds. Units swallowed by Tahm Kench are untargetable for a brief second after being regurgitated. _
Having his healing with grey health have a cooldown allows Tahm Kench's enemies to have opportunities to go in on him as well as giving Tahm windows to fight. Being untargetable briefly after being regurgitated, give both enemies and allies time to reposition, enemies especially, to see who and what is around them. Note that these changes are just his passives being shuffled around and giving his healing a cooldown.