Homebrew
Destructible Arms. Sentron has six arms. If Sentron takes 17 or more damage in a single turn, it loses one of its arms. The maximum number of attacks Sentron can make on its turn is equal to the number of arms it has remaining. If Sentron loses all of its arms, it regenerates all of them at the start of its next turn.
Multiattack. Sentron makes six scimitar attacks or three slam attacks. Scimitar. Melee weapon attack: +11 1d20+11 to hit, reach 10ft, one target. Hit: 14 (2d6+7) 2d6+7 slashing damage. Slam. Melee Weapon Attack: +11 1d20+11 to hit, reach 10ft, one target. Hit: 21 (3d8+7) 3d8+7 bludgeoning damage.
Setron can take 1 legendary action, choosing from the list below. Only one legenday action can be used at a time and only at the end of another creature’s turn. Setron regains spent legendary actions at the start of its turn. Summon Simbims. Sentron summons 0 (1d4-2) [roll:1d4-2} Simbims into any unoccupied spaces within 80ft of itself that it can see. Flurry Rush. Sentron moves up to half of its movement in any, straight direction, making a scimitar attack against any creature that enters its range. The number of attacks it may take is equal to the number of arms it has remaining.
Temfala Tower. Sentron's boss arena will contain six pillars situated around the edges of the room. If any one of Sentron's attacks make contact with one of said pillars, the pillar will crumble to the ground, potentially crushing any creatures caught underneath. All creatures within 10ft of a collapsing pillar must succeed on a DC 15 Dexterity saving throw or take 22 (4d10) 4d10 bludgeoning damage, halved on a success.