I just updated this mod to v6.6. Now the "Health Drain" feature can be set independently from a text file, so it becomes easier to find than reading the whole chat list one by one. You can check the changelog for the details.

I think what chiaranyan meant is the health drain, as that's the main problem of your review. & it's possible to disable that, as I provided the toggle chat commands in the chat list. It's the "special infected health drain off" like I said on the previous comment. While exp system doesn't affect at all whether it's enabled or not, just as I explained before, as the "health drain" will still work unless it's disabled with "special infected health drain off" chat command.

Btw, in case if you don't understand what I explained about "health drain" on comments above, type this in the chat box during play:  "special infected health drain off". That will disable "health drain".

And bots can't buy anything if you disable the "Survivor Bot Autobuy" even if they have enough exp points to buy items/ weapons. That's why I said exp system didn't affect the game.

Actually exp system doesn't affect the game at all. What affects the game for the current version is the "Survivor Bot Autobuy System" because that one is enabled by default. But that one can also be disabled via chat command. Check the Chat List no. (063) & (064). Probably you can also check other chat commands there in case if there are new chat commands you don't know yet. New chat commands are usually near the bottom of the chat list.

There are at least 3 options I provided there to fight a tank with "health drain" passive ability:
1. Disable the health drain via chat command.
2. If you don't disable "health drain", buy the skill "Special Killer" that gives a low chance to deal 10% of enemy's total health when triggered (if tank's remaining health is 4000, you deal 400 damage when this skill is triggered).
3. Like no. 2, if "health drain" is not disabled, burn the tank & fight from distance, & never let him damage you or other survivors.
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Actually the tank in the version when "Special Infected Autobuy Lv1" is enabled will be scarier (only if you enable autobuy for special infected), as he will also has several counterattack skills bought from "Special Infected Buy Menu". But I disabled that one by default, so that only when players want to challenge the more difficult special infected & tank, they can try to enable it via chat command.

Try to check the chat list no. (070) & (071) for that.

Did you read some comments below or the changelog? I think I discussed with someone there about that & later I updated a chat command to disable it. That power is called "health drain", that each time tank damages a survivor he heals certain amount of health. Disabling exp system won't make it stop as the chat command is different. Check the changelog about "health drain" if you want to disable it.

thats really odd, none of my testers reported that... have you tried again? like, to see if happens consistently