- ongoing 25 damage + slow, first save (remove slow and reduce ongoing damage to 15), second save (ends)
- ongoing 10 damage + slow, first save (remove ongoing damage), second save (ends)
Monster A Turn 1: Monster applies effect #1 to Bob. Bob is slowed.
Bob Turn 1: Takes 25 damage from effect #1. Makes save against effect #1. After the save, Bob still has "slow and ongoing 15" from effect #1 on him since he made the first save.
Monster B1 Turn 1: Monster applies effect #2 to Bob (poor Bob). Bob is still slowed due to effect #1, but stacking "slow" from effect #2 does nothing.
Bob Turn 2: Takes 15 damage from effect #1. Bob takes 10 damage from effect #2. If the ongoing damage type from these effects were both the same (such as fire) then Bob would take 15 damage only (the larger of the two ongoing damage amounts). Bob makes save against effect #1, ending effect #1. Bob makes the save against effect #2. However, Bob is still slowed from #2.
Monster B2 Turn 1: Monster applies effect #2 to Bob, who is still under the secondary save effect from the same effect from Monster B1. Effect #2 that was applied to Bob (that he has just saved 1 out of 2 against) is wiped out, and replaced with a new instance of effect #2.
Bob Turn 3: Takes 10 damage from effect #2 from Monster B2. Bob saves against #2 (first time for this instance) and no longer will take ongoing damage, but is still slowed.
Bob Turn 4: Has no more ongoing damage stacked on him, however is slowed. Makes his second save against #2 from B2, and is cured of all save effects.