#5ecard asks

Hey there, thanks for saying so! I'm happy to help out. I understand the difficulty too-- token generators are always tricky to convert, especially if there doesn't seem to be a good in-lore explanation for the way the abilities of the card mesh together. Since you mention doubling, I'm going to assume we're talking Krenko, Mob Boss (although I think any advice I give here could work for Tin Street Kingpin too).

My first thought is to connect the ability to Krenko's position as a gang leader, and perhaps to the idea of inciting a riot. For that, I would actually set the ability as a lair action, or just a function of the environment. For the former, give Krenko a lair action that calls up one goblin for every goblin who's already shown up. Maybe they all call for friends. Count Krenko too-- so he summons one pal, then next round they both summon another, then next round you get four more. Each goblin knocked out is one that can't call an ally, and they can all flee if Krenko is beaten. If it's a function of the environment instead, perhaps with a battle set during a goblin riot, use a clock. Each round on initiative count 20, for each goblin on the map, another one shows up. Be explicit about that, and let your PCs know that as long as Krenko and the other goblins run wild, things will keep getting out of hand. In both cases, you could allow Krenko to use a legendary action to direct the actions of these goblins, but otherwise they might loot, trash buildings, and generally cause havoc (including sometimes attacking PCs without being ordered to).

Straight up giving Krenko an ability that summons additional goblins also isn't a bad idea, but you could describe them as appearing out of alleyways, climbing up through storm drains, popping out of crates and barrels, dropping in from higher levels of the city, etc. Really go all-in on the traditional "goblin warren" type of situation, maybe make a d10 list of places they show up and roll it whenever you need to describe them appearing. Also, give a reaaaaaaally big range of where a "summoned" goblin could appear relative to Krenko. Maybe just anywhere on the map, setting them up for sudden attacks against PCs who thought they had good positioning. If you do with this option, I'd set it as a recharge ability, with the number of goblins depending on Krenko's CR (somewhere between 1d4 and 2d4). If you do, to get a semi-accurate read of Krenko's CR just add each goblin's flat HP and average damage to Krenko's own. So for example, if he summons 1d4 goblins (an average of ~2) with each use of the recharge ability just add 14 extra hit points and 10 damage/round to Krenko's stats when calculating his CR (using the normal assumption of three rounds of combat as listed in the DMG).