Glasc Mixologist

Yes, because Glasc's [Deathknell] chooses its target only after every unit killed by the same event has moved to its owner's trash; at that point, the target must be a unit card in your trash with an Energy cost no more than 3 and a Power cost no more than .^403.2429.2 The ability becomes pending before Glasc moves to the trash, but no target is chosen until the ability finalizes.^808.1.d.2 A killed token instead ceases to exist immediately after entering the trash, so it cannot be targeted.^186.1

During a cleanup, units with lethal damage are killed and moved to their owners' trashes before pending abilities can finalize.^{323.4320334.2}

When one effect instruction of a resolving spell or ability kills multiple units, their deaths are simultaneous.^370.1.a.2 No pending ability can finalize until the current spell or ability finishes resolving.^158.3

Yes, as long as you controlled that battlefield when Glasc Mixologist died.

Outside a showdown, Glasc's [Deathknell] is added as a pending item before he moves to the trash, and any cleanup already in progress or caused by his death finishes before that ability can finalize.^{808.1.d.2320334.2} That pending ability keeps the chain in progress throughout the cleanup, so you do not lose control of the battlefield even if Glasc's death leaves it empty.^{330309.1323.5} You can therefore choose that battlefield as a valid destination when the unit is finalized.^355.2.a

During a showdown, control of the battlefield cannot change until instructed by the steps of the combat or showdown, so you can likewise choose that battlefield as the unit's destination.^190.4.b

The original combat result is determined only after Glasc's chosen unit enters and every associated chain item finishes.^468.2 At that point, the result depends on which players have units at the battlefield:

• Only your units remain: You win the original combat.^468.3.a
• Only your opponent's units remain: Your opponent wins the original combat.^468.3.a
• Both players have units there: Neither player wins, and a new showdown and combat are staged.^{468.3.d468.3.d.1}
• Neither player has units there: Neither player wins, and no new showdown or combat is staged.^{468.3.d468.3.d.1}

Steps

1. The combat cleanup heals all units before Glasc's pending [Deathknell] can be finalized.^{468.1.a.1320334.2} Because Glasc was your only defender, no defenders remain during cleanup, so the surviving attackers are not recalled.^468.1.a.2

2. After the cleanup, Glasc's [Deathknell] resolves and begins playing the chosen unit. The unit becomes pending while the ability finishes.^354.2354.3

3. The unit then finalizes and enters the battlefield exhausted.^359.2.c Any play effect and other resulting chain items also finish before combat result is determined.^{383.4.a.2468.2}

4. The players' units then determine who won the original combat and whether a new showdown and combat are staged.