"Clean" way to inflict continuous damage

[Apeirogon]

Is there are any "clean" way to damage some monster some certain amount of time, like burning?
I can use overridden do effect inventory virtual, which damage its owner every tick and given to monster on attack. But I want to know is there are another way to do so with build in functions.

[hideousdestructor]

I don't think a truly "clean" method exists.

My own favourite at the moment is to have a projectile continuously call DamageMobj against the actor it has hit until it runs out.

[ZzZombo]

Given you already somehow have the reference of the target actor:

• Call an ACS script on it to damage it. Can easily configure damage interval, damage amount and duration.
• Make it launch a static, invisible and otherwise harmless missile that hurts its target in a possibly looped state sequence. Can also configure those properties by tweaking the state sequence; by warping it to the actor and giving an appropriate appearance you can also display "burning" FX. You can force the victim launch the said missile even w/o making any changes to it by giving it a `CustomInventory` that calls missile spawning function in its `Pickup` sequence.
• A variation of the above, spawn a regular actor instead of the missile and save the victim in an actor field such as `master` and then act on that reference. This is less hacky since it doesn't abuse missiles into doing something they weren't designed for, but requires to store and manage the reference to the victim yourself.
• In ZScript, you have much better ways, like a custom `Tick` override to do damage given some variables set on the actor, a dedicated `PeriodicDamage` routine, etc.

[hideousdestructor]

I'm going to take Graf's response here as the "official" recommended way to do it, inasmuch as any exists especially given his comment at the end:

You do not need hacks. What you need is a thinker that periodically inflicts the damage. Internally I couldn't do it any other way.

[Apeirogon]

I try to do example for this, but I cant understand how make ticking thinker.

[Graf Zahl]

Every thinker ticks, unless you change its statnum to something explicitly non-thinking.