#1 The Undertaker

The Undertaker recently fought at Extreme Rules and he is expected to be part of SummerSlam which is the Biggest Show of the Summer. The Phenom could be an excellent choice to face McIntyre. Since the Deadman was the Tag Team partner of Roman Reigns, the former crossed paths with McIntyre at Extreme Rules.
Though Undertaker skipped WrestleMania, he had a dream match at Super ShowDown where he faced Goldberg. However, the dream match turned into a disaster with several botches. During his recent match at Extreme Rules, the Deadman seemed eager to prove his doubters wrong and he delivered a great performance.
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The Phenom and The Scottish Psychopath had a face-off at Extreme Rules. Due to the age of the Undertaker, he might not match the swiftness of McIntyre in the ring but they could offer a decent match. Regardless of the result of the match, it could elevate the stature of McIntyre in the WWE.