Maxine Newman's clarification on the effects of the tokens:

This is a bit of a tricky situation so I will outline it step by step, as best I can. =)

Rex’s Curse triggers during Step 6, when you determine success/failure of the skill test. By that time, some chaos token effects will have already triggered. Chaos token effects that say “if you succeed" or "if you fail” will not have triggered yet, as Rex’s Curse interrupts the timing of those effects, but since Rex’s Curse does not cancel or ignore the token (like Wendy’s Amulet or Grotesque Statue does), the token will have created a delayed effect that will trigger during Step 7, regardless of whether the token is returned to the bag or not. Chaos token effects that simply have an effect (like “Place 1 doom on the nearest Cultist enemy,” for example) trigger during Step 4, before Rex’s Curse triggers.

After you return the chaos token and draw a new chaos token from Rex’s Curse, the sequence returns to Step 3, and you should follow the sequence in order as normal.

So, in your example:

• You draw the cultist token during step 3. During step 4, you place 1 doom on the nearest cultist, as part of the token’s effect.
• When you would pass the test (during step 6), you return the revealed chaos token to the bag and reveal a new chaos token. This returns you to step 3 of the sequence.
• You draw another cultist token! Poor Rex. During step 4, you place another doom on the nearest cultist.
• Step 6 rolls around again and you pass the test, so Rex’s Curse remains in play.

Had you revealed a chaos token that says “If you succeed / if you fail” during your first reveal, it might go like this:

• You draw the hypothetical token during step 3. It says “if you fail, take 1 horror.” This creates a delayed effect that will deal you 1 horror during step 7 if you fail the test.
• When you would pass the test (during step 6), you return the revealed chaos token to the bag and reveal a new chaos token. This returns you to step 3 of the sequence.
• You draw another hypothetical token. This creates another delayed effect that will deal you 1 horror during step 7 if you fail.
• If you failed this hypothetical test, during step 7, you would take 2 horror (one from each of the tokens).

I hope this clears things up. Cheers!

Not a review but to clarify rules on this tricky card: when you return the token, its effects are not canceled, but its modifier is. So you apply the modifier of the second token, but the effects of both. (edit: this include both tokens that have effects that apply immediately when you pull them, as well as tokens having delayed effects, such as "if you fail"). To fully understand this interaction you should read the skill test timing chart in the rules reference!

This is a fairly unique signature Weakness, annoying but persistent. Looking at the two elements, the effect and the discard condition, we get:

The effect: fairly simple -- if you succeed, return the token and draw another. This has the unfortunate result that you slow down the game a bit drawing tokens and then redoing the test, keeping track of possible stacking token effects. On Hard/Expert, this can give you lots of extra chances to trigger bad token effects, but it's more manageable in Easy/Standard where the annoyance of going back to the token bag repeatedly is maybe greater than the actual mechanical effect.

The discard condition: Fail a test. However, that just puts it back in your deck. Given Seeker card draw, it's not unlikely you will see this over and over.

All in all, this is an average signature weakness, maybe above average on harder difficulties. it can end scenarios by piling on Doom, Horror, or Damage in worst case scenarios.