Here's what rhymes with dumbfounded.

Consider these alternatives

mystified / side astounded / grounded perplexed / next mortified / side amazed / based horrified / side appalled / called awed / thought dismayed / made bemused / used pained / change overjoyed / avoid dejected / rejected elated / created stupefied / side annoyed / avoid peeved / received stunned / and aback / back amused / used