Contradiction with Matthew 21:2
In both verses, Jesus instructs disciples to find a donkey, but Matthew references a donkey and a colt, whereas Mark mentions only a colt.
Matthew 21:2: Saying unto them, Go into the village over against you, and straightway ye shall find an ass tied, and a colt with her: loose [them], and bring [them] unto me.
Contradiction with Luke 19:30
This verse mentions Jesus asking for a colt in a similar scenario, but it's noted as already tied, not being brought to Jesus for the first time as implied in Mark.
Luke 19:30: Saying, Go ye into the village over against [you]; in the which at your entering ye shall find a colt tied, whereon yet never man sat: loose him, and bring [him hither].
Contradiction with John 12:14-15
This passage speaks of Jesus finding a young donkey himself, without mentioning the instruction to disciples to fetch it, differing from the directive in Mark.
John 12:14-15: And Jesus, when he had found a young ass, sat thereon; as it is written,
Contradiction with Matthew 21:3
Mark mentions a specific phrase Jesus tells the disciples to use if they are questioned about taking the colt, whereas Matthew generalizes it without a direct quotation.
Matthew 21:3: And if any [man] say ought unto you, ye shall say, The Lord hath need of them; and straightway he will send them.