Incorporeal Movement. Tom can move through other creatures and objects as if they were difficult terrain. It takes 3 (1d10) force damage if it ends its turn inside an object.

Shield of Arrow Catching. Tom adds 2 AC against all ranged attacks against him.

Control Earth and Water. Tom can cast Stone Shape and Water Wall once a long rest.

Spellcasting. As to help with being a host, Tom is a 3rd Level Bard. Spell DC 16, and +8 to attack. He has the following Bard spells prepared:

Cantrips: Mage Hand, Poison Spray, Vicious Mockery

1st Level (4 slots): Comprehend Languages, Cure Wounds (can be cast at 2nd level), Disguise Self

2nd Level (2 slots): Enhance Ability, Locate Object, Suggestion

Multiattack.  Tom can Life Drain and shield bash, or use Trident twice.

Life Drain. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 23 (4d10 + 3) necrotic damage. The target must succeed on a DC 16 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Create Specter. Tom targets a humanoid within 10 feet of it that has been dead for no longer than 1 minute and died violently. The target's spirit rises as a specter in the space of its corpse or in the nearest unoccupied space. The specter is under Tom's control. Tom can have no more than seven specters under its control at one time.

Shield Bash. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 10 (3d4 + 4) bludgeoning damage. If the target is a Medium or smaller creature, it must succeed on a DC 16 Strength saving throw or be knocked prone

Vicious Trident. Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. and range 20/60 ft., one target. Hit: 8 (1d8 + 4) piercing damage, or 16 (3d8 + 4) piercing damage if used with two hands to make a melee attack. When Tom rolls a 20 with this weapon, add 7 to the damage.

Parry. Tom adds 3 to its AC against one melee attack that would hit it. To do so, the gladiator must see the attacker and be wielding a melee weapon.